A Friend ordered a 16" midlength 5.56 Nitride barrel upper with PSA 13.5"  M-Lok rail.  There is a hole at the rear of the M-Lok groove at position 3 & 6 O Clock.  There is also hole next to the M-Lok groove at the muzzle end of the hand guard.  Are these holes compatable with the Quick Disconnect sling swivels or is there an insert that goes in the hole to accomodate a QD sling swivel?   I looked and haven't any found a swivel sockets that fits in the hole.  Most of the swivel socket holes have a groove to accomodate the detents on the QD sling swivel.   The PSA hand guard is just a hole with no groove on the inside of the hole for the QD swivel detents.   I'm concerned the QG swivel might not hold in the hole that is machined in the PSA hand guard.   Any insight would be appreciated.  I provided a link to the upper my Friend purchased.


http://palmettostatearmory.com/psa-16-mid-5-56-nato-1-8-nitride-13-5-lightweight-m-lok-freedom-upper-no-bcg-or-ch-516445825.html

The holes in the rail are the QD sockets, there's no additional insert.  The inner face of the rail acts as the locking surface for the QD swivel, a lot of QD sockets on rails are done this way.  Only downside is they are not rotation limited.

Thanks for the reply.  That makes sense because I know the QD socket on a Tavor limits rotation of the swivel.   Seemed like it should've worked but never had access to a hand guard so equipped and a QD sling swivel at the same time.   I'll let my Friend know he can now use QD swivels in those locations.

.. and it tends to scratch the hell out of anodizing (using those holes usually scars up a 6061 tube something fierce).

I kind of figured the sling swivel and sling would sctatch the anodized finish.  I'm not sure my Friend is going to use the holes on a regular basis but at least he'll know they'll work.