Screw Threads in Top of Handguard

[SpitNine]

Finally got around to sorting those out although I have no use for them right now.
I use the term Heli Coils, which is a brand name, as a convenient description of threaded inserts only. There are several other brands of inserts.
The kit I bought was not a Heli Coil brand kit.


The threads in my upper, a Wolf A1, are 4x0.7 mm.
And they are Heli Coil type inserts.
I tried to screw in 4mm screws but could get them in no further than one or two turns.
Turns out there was a significant amount of what looks like red Loctite in the threads,
So, got a 4x0.7mm tap and tried to clean out the threads.
Didn't work. The tap, instead of cutting the Loctite and cleaning out the threads, got stuck in the Loctite and just pushed the Heli Coil insert out of the handguard metal insert. The thread left with the Heli Coil pushed out is a non standard one specifically designed for use only with Heli Coils.

So I bought a 4mm Heli Coil kit from Amazon and installed two new 4x0.7mm inserts the same length as the original ones. Obviously I did not have to use the special tap that came with the kit because the proper threads were there already. Super easy install, worked fine and 4mm screws now turn easily by hand.

I did put a very tiny drop of red Loctite on the handguard threads before installing the new inserts. It did not bleed through.
HTH.
Stay Safe.