January 2011: I have not been keeping up with the specifics of this FAQ for quite a while. There are now so many different types of AKs on the market and the SARs are a rarity. Please keep in mind that was written in 2003 and that your specific AK may be completely different; there's just no way to know with specificity what exactly is going on with the front of your barrel without checking.





I've posted this on another "ahem" AK website, and thought it might come in useful here too.... I'll start the general FAQ, and everyone else can chime in with their corrections/additions/personal anecdotes.





1) Diameter of barrel





Most SAR-1 and SAR-2 rifle barrels are 14mm diameter, although it does vary slightly from rifle to rifle. SAR-3 rifles usually have 1/2" diameter barrels. Non-standard sizes will have to improvise. I have recently heard of and finally seen with my own eyes that the diameter of some SAR's can vary from the FSB forward. At a recent gun show, I saw 4 laminated SAR-1's laying side-by-side. One of those had a noticeably thinner barrel from the FSB forward. This barrel will be too thin to thread.





2) Type of muzzle brake





The two most common variants are the "slant" brake and the AK-74 style muzzle brake. Figure out which one looks better to you. SAR-1's look most authentic with the slant brake, SAR-2's mate up with the AK-74 brake. There are AK-74 style brakes which will work for an SAR-1 also.





AK brakes come in different internal thread diameters and and thread pitches. Common are 14mmx1 LH (Most common, used by slant brakes, aftermarket AK-74 "style" brakes, and polish Tantals), 22mmx1.5 LH (unique to Romanian AK-74 muzzle brakes), and 24mmx1.5 LH (AK-74 brake).





I don't know if there are any "genuine" AK74-style brakes in 5.45 caliber which thread on 14mmx1LH barrels. This would be important to someone with a SAR-2 trying to keep the correct AK74 "look" by threading the barrel. There is a smaller US made brake, but its external diameter is quite a bit smaller than the real thing and doesn't look authentic.





3) Attachment to barrel





Muzzle brakes are available in many different styles. The most common are ways to attach them are:





(a) Set screws





The cheapest, but not the sturdiest way to go the muzzle brake route. The internal bore of the muzzle brake should slip over the barrel with a tight fit, or you'll have to shim it. Either way, it is highly recommended that the barrel be dimpled under the set screws. Dimpling is accomplished by carefully drilling into the barrel just deep enough to leave a little crater for the set screw to "bite" into.





To make a muzzle brake with slip-fit properties, you can either buy a brake which has no threads and fits tight, or you can use a Dremel tool to grind off the threads. in the latter case, you'll have to make sure the brake slips on concentric to the bore. You can drill and tap the brake for any number of set screws yourself if you have this ability. If all else fails, you could probably still have someone weld it on for you so it stays put.





Dynasystems can make brakes with custom internal bores and set screws, and they also have an adapter which has set screws to attach to the barrel, and has 14mmx1LH threads so that you can thread a muzzle brake to the adapter.





Set screw muzzle brakes are the cheapest way to do it (usually), but they have the problem that the gases they redirect also cause them to slip off the barrel and fling them down the range, especially with the 7.62 caliber guns. Read the Dynasystems page where they talk about the thread adapter for more info. The barrel dimpling method is supposed to work pretty good though.





(b) Threaded barrel





SAR-1's do not have threaded barrels. WASR's do no have threaded barrels but a muzzle nut which is pressed on and welded. Cutting off the muzzle nut usually won't work as witnessed by several people on the board. Do a search on the board to find out what the problems are. CORRECTION: There's no way to really determine what your WASR's muzzle might look like; it probably depends on what the Century monkeys had laying on their desk that day. I'll avoid making general commentaries; you'll just have to inspect it and see what you get.





A lot of gunsmiths won't try threading the barrel. They're probably thinking of chucking up the rifle on their lathe, and that's not easy. The tool best used for this is something you can do at home. Dynasystems sells a muzzle threading kit, which is also making its way around this board for rent. With this tool, you can thread your barrel to 14mmx1LH, although it's available in several other sizes also. SAR-3's usually come in 1/2" diameter barrels, which is also common with AR-15's. Those are usually threaded 28tpi. The threading kit costs $60 if you purchase it, while rental fees are usually in the $10-20 range.





It may sound scary to do that to your rifle, but it's fairly easy. Just be careful and follow the instructions. The die cuts the barrel fairly easily. If you're curious, here's what the instructions consist of: preciseinnovationsllc.com/GunFile/ThrInstr.html





The problem is that now you have a threaded barrel, which won't make the BATF happy if you live in a state with its own AWB. You'll have to attach the brake in such a way as to make it permanent, at least as far as the ATF is concerned. More on that later. The rest of you rejoice - you're good to go.





Once the barrel is threaded, you can directly thread on a 14x1LH threaded brake. You can also get an adapter bushing which has 14mm internal threads and 22mm or 24mm external threads to allow threading on the larger brakes, which will in turn allow you to attach AK74 brakes.





If you have a threaded barrel, you will also want to install the dentent spring and plunger if yours is missing. This will prevent your muzzle brake from twisting off. All AK muzzle brakes (if I'm not mistaken) have a notch which will index on the plunger sticking out of the FSB. You can order something like this set from Globaltrades or you can make your own out of a small piece of steel rod and a spring of the proper length. If you check this picture on K-Vars website, you can clearly see the hole in the front of the FSB just above the threads where the plunger and spring need to be installed. To do that, you will need to drive out the retaining ping enough to allow you to slip the plunger into place. The plunger has a notch ground out, which will keep it in place when the retaining pin is reinstalled. These pins are difficult to remove; they need to be hit quite hard, and with a strong pin punch. It's not necessary to completely remove the pin. Make sure your FSB is properly supported so that you don't twist it on the barrel. Tapping the pin back in is quite easy; simply drive it flush.





(c) Threaded FSB





This is covered by linx310's website: linx310.nothingbutguns.com/threadinstall.htm





Also check out that website for a home-made adapter. Personally, I find that too much of a hassle, but it's certainly innovative.





(d) MAK-90 brakes





These are available cheap, like $10 I believe, to fit MAK-90's. The problem with these is that they are supposed to be pinned on the FSB of MAK-90's, and the pins don't work for SAR rifles, and the barrel on the SAR's is too small. Nevertheless, several people have made it work, going the route on slip-on brakes with shims to widen the barrel diameter. You will also have to use a Dremel tool to cut a slot in the bottom of the brake to allow it to fit around the cleaning rod. Here's a thread with a successful conversion: www.gunsnet.net/forums/showthread.php?s=&threadid=80816





4) Legal issues





(a) General disclaimer





Obviously I'm not reposible for anything legal, so all of this is done at your own risk.





(b) Parts count





To stay legal in the ever-popular parts count sham, you'll have to replace a foreign made part with a US made part on your rifle if you add a foreign-made brake. If you add a US brake, you're fine.





(c) Legal attachment of muzzle brakes to threaded barrels





The paragraph below is not needed in those states where the AWB has expired. Please make sure you check your local laws before leaving a threaded barrel exposed.


Since having a threaded barrel will incite you to obtain silencers and go on shooting rampages, you'll have to "permanently" attach your brake to the BATF's satisfaction. This can be done by several methods: Spot welding, which is kind of ugly and will discolor the metal due to the temperatures involved, and is somewhat permanent depending on how its welded. The second is to use high-temp (1100deg) silver solder. This will also discolor the metal, but has the advantage that it can be easily reversed if the AWB sunsets. If you have the right equipment, you could do it yourself. The third is a blind pin drilled though the brake and into the threads of the barrel which is welded over and ground flush. The re-bluing can be easily done at home and if the AWB sunsets, you could cut off the brake. This method is fairly cheap - I paid $20 at a local gunsmith.





The correct way to attach brakes is via a plunger/spring which fit into the FSB. The are available from KVAR and Global Trades among others. You need to drift out the pin closest to the muzzle on the FSB. These pins are very tough amd need a pretty good pounding to get them started. DO not use a long pin punch for this method. A nail set worked for me. Once the pin has budged, you can usually use a pin punch to drift it out a little further. It doesn't have to be completely removed, just drifted out far enough to allow the spring and plunger to be inserted. I used a Bulgarian set, and the plunger was a little too long, so I had to grind it down about 1/4". Be careful to not take off too much material such that the pin won't be held in by the FSB pin anymore. When you look at the plunger pin, you'll know what I mean.





More information on 22mm threaded barrels/FSB, please refer to www.gunsnet.net/forums/showthread.php?s=&threadid=59131





5) Sources





Here are some sources of muzzle brakes and various parts:


www.dynasystems-ltd.com


www.globaltrades.com


www.krebscustom.com/CustomParts.html





And some others. I'll let the community fill in. Please add to/correct this information to keep it current.

 

Very good Zhukov!- Hardly worth mentioning but there was one exception. That exception was the grandfather clause of the 1994 act. If you owned it prior to 13sept94 it was generally understood that you could run threads on the barrel, change to FSBs,etc This was much prior to the American parts rule! It applied to the Mak90 but the statute of limitations on that provision has run out and AK weapons are best considered post 94 ban, presently.

Originally Posted By Zhukov: Obviously I'm not reposible for anything legal, so all of this is done at your own risk. (b) Parts count To stay legal in the ever-popular parts count sham, you'll have to replace a foreign made part with a US made part on your rifle if you add a foreign-made brake.

Zhukov,
I'm a newbie that just bought a Romanian SAR2.  I'm wondering about the guidline above.  I'd like to keep this baby as "authentic" looking as possible.  Seeing as that I'd like to replace the wood furniture, trigger group, and sights (not sure with what) anyway, can I then added a foreign made brake?

Thanks for the help.

EDIT: By "authentic" I don't mean Romanian.  If it looked like something a Russian Spetnaz soldier might carry (if not issued an AN-94 heheh) that would be pretty cool.  Perhaps black furniture and a red-dot sight or whatever they might use.

Also, thanks for the great info!

Hopefully someone will chime in on this quickly as I'm dying from curiosity here. I picked up a slant brake this past weekend for my SAR1 and I asked the shop owner if the brakes were "US" made and he said yes, but really, there are no markings of any kind on the brake, so how do I REALLY know this brake is US made? I would hate to be in a situation with an LEO and it's his word against mine and were both staring at a slant brake that has no markings.

(d) MAK-90 brakes These are available cheap, like $10 I believe, to fit MAK-90's. The problem with these is that they are supposed to be pinned on the FSB of MAK-90's, and the pins don't work for SAR rifles, and the barrel on the SAR's is too small. Nevertheless, several people have made it work, going the route on slip-on brakes with shims to widen the barrel diameter. You will also have to use a Dremel tool to cut a slot in the bottom of the brake to allow it to fit around the cleaning rod. Here's a thread with a successful conversion: www.gunsnet.net/forums/showthread.php?s=&threadid=80816

I was thinking about having my machinist workup about 25 or so of these with bushing material included in a kit for $25. They are AK74 type brakes and would require finish fitting by yourselves or a gunsmith.  The cuts to fit the Romanian AK's SAR-1 and WASR-10 would be made.  It would require the bushing, pinning and final inspection to make it ready. Look over the above thread and if anyone is interested let me know.
thanks

ok so read the how to on ak47.net, but I have questions. I have a WASR-10 and a AK74 MAK brake(pin on).  I had the bottom machined so it would pass the the cleaning rod lug.  The difference in size of barrel I used the info on the AK47.net page. I used brass shim .003  Mine need more wraps than he stated with his SAR-1.  Mine is on there, but there has to be a better way.  How do you get the shim stock to stay in place while your trying to size it??? I was even thinking of using bedding compound and bed the muzzel brake to my barrel (using releasing agent on the barrel of course) I was afraid if I bed it, it would settle off center.  So maybe if I bed the muzzle brake I should run a rod thru the barrel to keep it aligned.  Anybody else got any suggestions for the MAK brake on the WASR-10?

Well, after running back and forth about what kind of muzzle brake to get, I went with a -74 style MAK-90 brake for my WASR-10 from Tapco ($19.99 US Made).  I simply cut out a notch for the cleaning rod with a dremel and it fit on very good.  Then I lined it up straight (it was already really straight because of the notches) and MIG welded the top and sides of the front sight block to the brake.  If you know how to weld or know a friend who does, this is a very easy way to do it.  About 10 minutes, $20, and no running to the store for shims.  Here's a pic of the completed product.


http://ovrdrivn.com/gunpics/muzzlebrake.jpg

Thank you Zhukov! The info was very helpful. Now that the AWB is gone do you plan to make an update to help those who are confussed?

Maybe mention that [email protected] is one of the guys out there who is renting a threading kit?

Those who want to rent threading kit email wjm at address above.

Originally Posted By Hatchet36: Thank you Zhukov! The info was very helpful. Now that the AWB is gone do you plan to make an update to help those who are confussed? Maybe mention that [email protected] is one of the guys out there who is renting a threading kit?

Already done, I think....

I haven't added WJM as the threading kit rental guy, but I suppose you just did.

Just wanted to let you all know that I have a WASR-10, which has a threaded barrel. I just received it a couple weeks ago and decided to find out if the slanted muzzle break was pressed on or threaded on. I ended up cutting the slant off with a dremmel (pain) because it would not turn off no matter how hard I tried, but I founded out it was indeed a threaded barrel.

So if anyone was interested in changing their Romanian muzzle break out, the new imports do indeed have a threaded barrel.  Or at least mine does.


Clip fed

So if I have a WASR with a welded muzzle nut, I'm shit  out of luck if I want to thread a brake on???

Hey Zhukov,
I fixed my WASR brake problem.
Sure I'll catch a flame for it though.
Check out the thread.
Wile E Coyote School Of Gunsmithing at it's finest or worst.

I was looking into the muzzle threading kit by Dynasystems a while back for my SAR-1, but then I heard that threading your own barrel with one of these threading kits decreases the accuracy of the rifle. The source that I was talking to said that the preferred method was to have the threads cut on a lathe.

Has anyone heard this? The muzzle threading kits sound great, but I've put the idea to the back burner for now. Woud someone please offer some clarification on this. Thanks.

Originally Posted By ChannelCat: I was looking into the muzzle threading kit by Dynasystems a while back for my SAR-1, but then I heard that threading your own barrel with one of these threading kits decreases the accuracy of the rifle. The source that I was talking to said that the preferred method was to have the threads cut on a lathe. Has anyone heard this? The muzzle threading kits sound great, but I've put the idea to the back burner for now. Woud someone please offer some clarification on this. Thanks.

The only way you would deteriorate the accuracy is if:
1) You mess up the muzzle crown somehow, or
2) The brake is installed crooked and the bullet actually hits the brake.

The alignment tool is what prevents #2 from occuring if you're doing it right, and I really don't know how you'd mess up the muzzle crown, unless you tried to shove an oversized TA in there and messed it up in the process. I think whoever told you that might have been a gunsmith who was afraid of losing some business.

Thanks Zhukov. As a matter of fact, I did hear this from a gunsmith. I think I may have to get one of these kits next month when I can afford it. It should work for both my SAR-1 and my Norinco SKS, both in 7.72 x 39mm.

This thread was very helpful. Gave me the courage to thread the barrel on my SAR1. It came out great. Dynasystems does not have any of the kits right now but brownells has everthing you need.
The lock pin and spring I bought from Numrich. Thanks again for the great information.

If you order all the stuff from brownells how much does it cost?  What items do you need?  Do you have to remove the front sight post?  I have a WASR10 I am planning to thread.  Any suggestions would help.

It ran $90 with shipping. A buddy and I split the cost ( we are doing his too). You need the handle, Die, thread alignment tool. It took about 10 minutes to do mine. I'm still waiting on the other brake to come in.

Originally Posted By Zhukov: (b) Threaded barrel SAR-1's do not have threaded barrels. WASR's do no have threaded barrels but a muzzle nut which is pressed on and welded. Cutting off the muzzle nut usually won't work as witnessed by several people on the board. Do a search on the board to find out what the problems are.

Just to let you know that's not allways true. I just got my Romanian AK and I cut the single tackweld off and found the barrel to be threaded with lefthand threads.

TAG

I've seen a slant break on some sites labeled as a flash hider. I looked this up this here http://en.wikipedia.org/wiki/Muzzle_break and found out that a muzzle break increases the report of the shot as well as the flash. Is that accurate? I imagine it is possible to take a muzzle break off a wasr-10 and replace it with a flash hider? My wasr-10 also had a threaded barrel. Thanks for the faq!

Originally Posted By dermofo: I've seen a slant break on some sites labeled as a flash hider. I looked this up this here http://en.wikipedia.org/wiki/Muzzle_break and found out that a muzzle break increases the report of the shot as well as the flash. Is that accurate? I imagine it is possible to take a muzzle break off a wasr-10 and replace it with a flash hider? My wasr-10 also had a threaded barrel. Thanks for the faq!

its not even really a brake. it is best defined as a "compensator". it only functions to reduce muzzle climb under full auto and reduce kicking up dust when firing from prone

I have an older WASR with a welded nut. It takes some careful work to cut the welds, I used a dremel and then tapped the nut off with a hammer and screwdriver. My barrel wasn't threaded, but instead, was turned down to a smaller diameter and could not be threaded. It was also longer than the typical muzzle length.

I cut the barrel 1/8" shorter with my dremel, cleaned it up with a file, and then crowned it with a carriage bolt in a hand drill using valve lapping grease.

Then, I slid on the slant brake, and drilled through the brake into the barrel just enough to leave a small dimple in the barrel.  I tapped the hole in the break and put in a set screw.  I JB Welded the whole thing, tightened it down, and then ground the set screw flush with the brake and painted it black.

When it was completed it looks correct. I also added a detent pin, even though it's non functioning.  

Looks perfect :)

most newer WASRs either have a threaded barrel with a nut welded on, or no nut at all.  

FYI, I have recently gotten a couple of Century WASR10's with the welded muzzle nut. I was able to remove the nuts with a Dremel...and both rifles had a threaded barrel (14 x 1 LH) and working pin. New brakes screwed right on without any problem.

I know this has probably been asked a couple times, but how do I know if my SAR 1 barrel has enough meat on it to be threaded?
Does anyone know how big the barrel needs to be?  Or a link to the info

Thanks

I cut the welded nut off of my new GP WASR 10 and the barrel was threaded 14x1mm LH.
Just FYI...

Originally Posted By clippen: I know this has probably been asked a couple times, but how do I know if my SAR 1 barrel has enough meat on it to be threaded? Does anyone know how big the barrel needs to be?  Or a link to the info Thanks

ok i just bought my GP WASR-10 it has the slant brake and dentent spring and plunger on the fs so does that mean it is threaded?i see no welded nut or anything just brake plunger and fs....sorry if i sound stupid but its my first ak and i am reading all i can on this great site


well after an hour of thought i figured i would give her a try taped a penny to the detent to hold her down pair of taped jaw vice grips and a hammer 25 seconds later one threaded barrel showing woohoo

I read this FAQ, then ordered a muzzle brake and a threading toolkit from

http://www.dynasystems-ltd.com     (Precise Inovation LLC)

Heard nothing back from them within except an automated email saying they received the order and charged $$. They do have a "Contact" email -- but they have never replied my query of order status.

Does anyone have experience with this company? Or knows their contact phone number in Utah?

I just picked up a WASR-10 last weekend and it has the welded on muzzle nut.  I'm curious to see if my barrel is threaded...but I'm a little nervous about taking the muzzle nut off.  Is there any practical reason for the nut to be on there?

I ended up cutting the nut off my GP WASR-10.  Barrel was indeed threaded.
Hooray.

height=8

Originally Posted By pcbme: I read this FAQ, then ordered a muzzle brake and a threading toolkit from http://www.dynasystems-ltd.com     (Precise Inovation LLC) Heard nothing back from them within except an automated email saying they received the order and charged $$. They do have a "Contact" email -- but they have never replied my query of order status.have

The toolkit arrived. Looks great!

just took the barrel nut off my wasr 10...not threaded

Any Detailed pics Step by Step Pics on How its Done .
im interested on threading my SAR1

This is my SAR-1.  Barrel was not threaded, front sight was welded in place.
Barrel was cut down to 13.5 inches.  Threaded and crowned.  Muzzle brake was silver sodiered in place.

Full details can be seen here:
hometown.aol.com/u873/AK47.html

http://hometown.aol.com/u873/images/sar-1%20with%20t%2074.jpg

http://hometown.aol.com/u873/images/romanian%20akm%20side%20folder.jpg

I've been the proud owner of a WASR10 for less than a month. If I can do it anyone can do it. Here is my noobie steps.

I decided to remove the muzzle nut off my WASR10. It was spot welded. If you look carefully you will be able to see the seam separating the nut from the front site on the topside of the nut. If you pretend to take a sharp knife and follow that line through the spot weld that is where you want to cut. I used a baby hacksaw to start a groove so I wouldn't damage the remaining section. Make sure when cutting that any material removed is on the nut side and not the barrel side.

It must have taken me over an hour to cut away what I thought was enough of the weld. Do it slow so that you don't cut away too much and hit the threads.

I sprayed some WD40 on the seam and let if sit for an hour. When I came back I used a clamp to secure a small screwdriver against the plunger to keep it depressed. Then I used a pair of vise grips on the muzzle nut. Gave the vise grips more that a few hits with a hammer (mine was clockwise to loose) before there was any indication it was actually moving and not just slipping. Finally after 3 hours total time (including waiting for the WD40 to work in) I got the muzzle nut off. VOILA!!! Threads.

I tested the threads with an old discarded crooked slant brake from another AK47 and the threads are indeed correct. BTW the muzzle nut exterior is ground up to hell from the vise grips. I temporarily put it back on the protect the threads until I get a new brake.

I have a Romanian Ak-47 7.62x39.  When I first got it they fitted a brake for me at the gunshow with the screws.  I shot it off once, and left it off.  The threads have been runied by the set screws.  The question is, it possible or usually successful to try and clean the threads back up with a threader? (The opposite peice of the tap what ever you call it).  I'd like to thread one on now that the ban is no longer.  I live in Michigan.  I believe it is legal to know have threaded brakes here.  

SAR-1 with a Type 74 muzzle brake.  Barrel was cut down, recrowned and threaded.  Last trip to the range I was getting a 2 inch group at 100 yards standing.

More info here: hometown.aol.com/u873/AK47.html

http://hometown.aol.com/u873/images/sar-1%20with%20t%2074.jpg

My WASR10 does not have threads. It seems that the threads have been removed. My barrel is now thinner than 14mm. I would love to install a brake, but now it doesn't seem possible.

Any suggestions?

I just ordered my threading kit from PI and my spare parts kit from akparts. I'm excited

Managed to get the compensator off my GP WASR10 with some considerable force. The thing is, it's not standard AKM. It has a right hand turn. On clockwise. Off counter. Standard compensators and blank adapters are too large for the threaded portion of the barrel. Threading gage says the thread pitch is 20. Diameter is roughly 15/32" or 12mm. Exposed barrel diameter is 14-15mm.

Anyone else heard of this? Any attachments that will fit?

Which muzzle brake fits the WASR-10 GP?

I've got an all black Romak underfolder. I like the AK74 muzzle brake look on it. Got it from TAPCO.

http://i73.photobucket.com/albums/i222/sdacbob/RomanianAK-4.jpg

I had a muzzle brake pinned on years ago.  The bullets must have been slightly hitting it as I eventually shot it off.  I sighted it in with a scope and the accuracy was much better.  I'd still like to use a brake.  My barrel is threaded but the threads were beat up by the set screws.  If I chase the threads would it clean up enough to screw on a brake?  

I have a Century GP WASR 10 that came with the slant brake. I have bought 2 different flash hiders and brakes that turned out to be too big for the barrel on this thing.

What size is this? Anyone know of a source for a flash hider or muzzle brake that will fit it?

I have a J-Tac47 brake from Primary Weapons Systems on my WASR. It had the slant on it and I can tell you the J-Tac does help with muzzle climb. They should pay me for as many times I have recommended it....14x1 LH thread and yes it is American.

height=8

Originally Posted By DiscipleGreg: I have a Century GP WASR 10 that came with the slant brake. I have bought 2 different flash hiders and brakes that turned out to be too big for the barrel on this thing. What size is this? Anyone know of a source for a flash hider or muzzle brake that will fit it?

Sounds like you have the same problem I have. I posted a rough size estimate a couple of replies up.

I just got my Romanian WASR-10 and it has the tack welded barrel nut, Badrat414
what did you do to remove the tack weld and barrel nut?  Also the front sight is canted a little to the right, it can't be straightened without removal fo the tack-weld first

bought my wasr-10 during the band.(no bells or whistles).bought the tat threading kit ak-74 muzzle brake and detet pin , sears provided the spring which i cut to fit, took about an hr to complete mostly to hammer out front sight pin.came out great

Clockwork your threads are probably the same as mine. They're 1/2"x20 tpi.

Originally Posted By kletus: Clockwork your threads are probably the same as mine. They're 1/2"x20 tpi.

I have one that is threaded 1/2 x 20 as well. I took an A2 flash hider, ran a 1/2 x 20 tap through it, as well as drilling the inside of it out to 25/64". I had it secured with a crush washer at first and then I notched it for the detent pin. It went right on and I haven't had any problems with it.