New to f/f rail installs and am contemplating a YHM free float (specifically thesmooth carbine length).  Noticed in their installation instructions that they recommend using a proprietary wrench (YHM-9621).  Is this absolutely necessary or just  nice to have for installing such?

I bought a standard armour's tool and the pins didn't line up.  They are supposed to, but I got a bad brand, I guess.  I went and bought the YHM tool online fairly cheaply.  It worked perfectly, of course.

With the YHM rails you have to tighten two different nuts.  The barrel nut can be tightened with a standard barrel nut wrench, but the jam nut needs a spanner wrench.  You can use a screwdriver/punch and hammer, but it messes up the finish a little bit.

You're talking about this, right?  I bought it shipped from somewhere (Amazon, Midway USA, etc) for $20-$25 bucks.

I installed the yankee hill todd Jarrett handguard.  I didn't buy there tool.  My armorors wrench worked well.  The holes lined up fine with the 3 pins on the wrench.  A little advice for you......you do not need to crank down on the jam nut super tight with a spanning wrench.  I tried doing that and I screwed up the jam nut.  Bought a new jam nut because it was driving me crazy.  You could see it was messed up.  Took a little advice from somebody on here and put a little electrical tape over the tip of a flat tip screwdriver.  Tapped it on tightly and that's all you need.  If that handguard has anti rotation screws its not going anywhere.  I believe I put a little wheel bearing grease on the threads also to aid in removal if I ever want to remove it.

thanks folks, will try without and buy it if I have issues.

Looks like the same handguard I put on something for someone. Used a PRI barrel nut wrench and a pair of pipe pliers. The pliers had a tooth at the end of the... claw or w/e that happened to fit perfet. I have a couple different brand pliers with that, so I think it's common. I then just used some cloth to lessen any scratching. Worked well.

Some people recommend using a stock castle nut wrench, but it scratched it and didn't work well. (There person this was for was ok with that as long as they didn't have to buy the special tool)

For the jam nut; just use a wide but sharp flat head screwdriver at an angle, and lightly tap it tight with a small hammer.

Be careful on the angle, as if it is too steep or narrow, you can mar the metal.  If you do that, it can be fixed with a small file and cold bluing.

I used a armorer's wrench to tighten the barrel and a flat head screwdriver.

That is all I needed.

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I used my standard armorer's wrench.  Worked for both.

I use a large chislel and it works fine.

Wish my original tool would have been in spec.  Sounds like everyone else's was.  Would have saved me buying this, but hey, at least I'm going to build more than one.  And with the tool, it locks in to place, so no knife or screwdriver needed.

Money well spent........I have this and used it install my YHM float tube........also worked on a Chinese copy........