Takes the little 4-40 set screw in their lpk holds the detent and spring in.

Pretty nice feature, if you are planning on changing stocks/buffer tubes imo.

You can find the set screws alone online fairly cheap thinking of adding a few to older builds.

I found they work on Stag and Spikes lowers but not the Anderson so far.

Anyone compiled a list or know of the mfgs. that they work /no work with.  Matrix , DPMS , CMMG, Stoner etc.?

I purchased a 4-40 tap and have used them on all different lowers including Anderson.

The 4-40 set screws are fairly cheap, you can get a box of 100 on line for about $10.

One of my favorite features of their lowers. Just a nice touch.

Didn't even think of tapping my own threads. Thanks!

Wont buy a lower without it.  Spikes and Aero here.

The Strike Industries end plate comes predrilled with a hex screw that works perfectly with the Aero lower. Prevents you from having to trim the spring to a shorter length.

Link

We recently had our own line of lowers made. They have that threaded hole as well as a threaded bolt catch pin. I think the bolt catch pin is a bigger game changer than the detent spring set screws . But anyway they are very nice features both of them.

Yep, I've been doing the detent hole mod for at least 30 years. Just started doing the threaded bolt catch mod when CDNN put the surplus DPMS catch pins on sale last year. Since then have modified all my ARs and those of many of my friends. Had a friend at a motorcycle shop make me t-handle extensions for the two drill bits necessary and ordered a six inch long 6-32 tap from Ebay. With the three tools I can drill and tap the holes in about five minutes. Beats the heck out of the original roll pin.