Depending on how the Spike’s Tactical slim handguard turns out, there’s a good chance that I may buy another YHM lightweight for my LMT 10.5” upper. I’m quite happy with the YHM Lightweight handguard. Sling mounts and endcaps are sold separately. I believe that the top and bottom holes are for the YHM endcaps, and the holes on either side are for the YHM screw-in sling swivel studs, but don’t use either an endcap or a sling swivels, so I’m not really sure. These holes are NOT QD sling swivel sockets for the swivels that release with a push-button. The YHM lightweight handguards have holes at the front end for screwing in YHM’s sling mount. The center of the rails are milled out to save weight. You may also note that the slots in the rails on the YHM lightweight tube are not marked ("T-Markings"). YHM Lightweight on Top, MI T-12 on Bottom Although, as you can see in the photo below, the MI T-Series handguards don’t have a slot over the lockring anyway, so it really doesn’t make that much difference. The lightweight YHM does not give the full-length top rail effect. If you are picky, it may take 2 or 3 tries to get the rails to line up just right, but the same is really true of most railed handguards. The 9mm upper is blow-back operated, and had no gas tube hole to use to align with the hole the barrel nut. The only minor issue I had was aligning the barrel nut so that the top rail of the handguard matched up with the rail on the upper.
The rail covers shown in some of my pictures were not included either. There were no tools or threadlocker included with the YHM handguard. The indexing screws for the YHM are slotted, where the MI handguard has allen-head socket screws.
The barrel nuts of the YHM lightweight and MI T-Series handguards are nearly identical. It installs just like the MI handguard, except that it has two indexing screws, at 3 and 9 o’clock, instead of just one at 6 o’clock like the MI handguard. Once I got the barrel nut/delta ring assembly, and front sight tower off the RRA upper, installing the new handguard was simple. The YHM wrench works fine on the Midwest Industries lock-ring also, by the way.
The YHM tool can not be used with a torque wrench, and would require a very large diameter pipe to use as a cheater bar for more leverage. The RRA and Model 1 barrel nuts were likely overtorqued, the RRA in particular grossly overtorqued. The torque-spec for the barrel nut is more that 30 foot-pounds, but not more than 80 foot-pounds in order to get the hole or notch to line up properly with the hole in the upper for the gas tube. The Model 1 Sales upper that I had taken apart before was almost as difficult to disassemble. When I got a new wrench back from PRI, it took a 3 foot length of pipe over my breaker bar before I finally got the barrel nut to come loose with a crack. I broke pins off my PRI barrel wrench trying to get the RRA upper apart ( related post, PRI barrel nut wrench).
I would not count on using the YHM wrench to disassemble your upper, as you can’t apply much torque with it, although it may be enough to install the new barrel nut. The YHM wrench has a spanner for the lock-ring at one end, and a barrel wrench at the other end. Along with the handguard, I ordered the YHM wrench.