Its as simple as it sounds. A single has one hook and a double has two. The hook is what holds back the hammer and releases it when the trigger is pulled. I would imagine more doubles are sold than singles. A single will drop right in, but the double will require the receiver to have an extra slot for the extra hook.

Quoted: Its as simple as it sounds. A single has one hook and a double has two. The hook is what holds back the hammer and releases it when the trigger is pulled. I would imagine more doubles are sold than singles. A single will drop right in, but the double will require the receiver to have an extra slot for the extra hook. home.earthlink.net/~mwsjb/pictures/trigger.jpg

I doubt more doubles are sold then singles.  I myself have bought about 5 single hook groups back to when Jerry Gordon was actually making them.  A double hook FCG only drops into a milled (such as Bulgarian) receiver or a Chinese receiver which was (stamped and milled) designed for the double hook FCG's.  Most people who buy one as a replacement for a Romanian SAR or WASR rifle are going to buy a single hook FCG than a double hook which will require notching their receiver.

Same goes for building on most of the U.S. receivers I would think, unless you have a Global Trades receiver (or a flat from some distributors) which is already cut for the double hook FCG.  Ewbanks receivers are cut for a single hook FCG.  I thought that OOW receivers were also designed for a single hook but it's been a long time since I've seen one and can't remember.

I think a lot of people buy the TAPCO G2 FCG's from DPHarms and the single hook is $5.00 cheaper so I believe that makes a difference to some who would choose the single hook for the cost savings.  

Quoted: ...I would think,...

Careful, that's all I was doing. :)

The Gordon Tech single hook FCG's were made as double hook and then the second hook was cut off on the early ones I bought.  The problem with that was that you had to modify the trigger or the receiver to get them to work in some receivers (I did anyway).  I opted for modifying the trigger and Jerry Gordon stated he would honor the lifetime warranty if it failed afterwards.  Of course Gordon no longer has anything to do with the FCG's anymore now.  

I've never had to modify one of the triggers now that the manufacturing has been taken over by TAPCO.

Quoted: ok, is one necesarilly better than the other? Does the extra hook add an extra factor of safety??

Originals were a double hook design i assume. They probably went to a single hook design later when they added the rate reducer/hammer retarder. Since you wont have this part on your FCG, you might as well get a double hook unless 1) its not authentic for your rifle, and thats something you care about or 2) it wont fit your receiver and you dont want to cut the notch.

Most feel double is smoother, but i doubt its much safer.

Quoted: ok, is one necesarilly better than the other? Does the extra hook add an extra factor of safety??

I would believe that actually a single hook FCG that has been polished (I do this with all of mine) would have a smoother take up on the trigger as it has less surface than a double hook FCG to create friction.  You would have to have a trigger pull guage and install both types in the rifle and measure each to determine which has the lightest pull.

If you are concerned about the trigger pull just get the Red Star Arms adjustable FCG.  I've got one and have never even used it in a rifle.  I went with a double hook G-Tech in my Bulgarian build because it was built on the Global Trades receiver.  I actually took it out of one of the Bulgarian milled receiver rifles I sold and none of the other rifles I had would take it without modification of the receivers or trigger.

Polishing out the bearing surfaces of the G2 FCG only takes a couple of minutes with a dremel and a polishing tip and will smooth out the trigger pull.   Use a cotton type tip and some jewelers rosin type compound which comes in some dremel kits or the rubber wheels.

Linx310's site has a guide on polishing a FCG

But, I have seen on my SAR1 where the there was enough slop to cause the single hook to kind of slide just a hair sideways as well as forward when pulling the trigger.  I did not see those effects when I installed a double hook trigger.  

Some of the side ways movement could have been the fault of the Century FCG (single hook).

And no, I did not miss the assembly tube (slave tube) in mine.

To be honest, the single hook in my WASR10 is pretty nice.  For ultimate safety, the double has to me more robust than the single as you have the extra hook in place.

However, in reality does it make a difference?  I would think not as the double hook was abandoned when the rate reducer was introduced, so the designers felt the extra hook was not really needed.