Mag Couplers?

[USGI]

I have to say after seeing thousands of used magazines on various auction sites, the nubs always seem to be in fairly good shape.

I've had a couple bad ones. My 1st carbine came with a NOS KSG and the nubs stripped about 1/4 of the way off after firing less than a box of ammo with it - failed to feed unless you held onto the mag. I've read that the process of forming and hardening the metal in that area was improved after early failures were noted. Look close and you can see differences in those areas between various mags. I've got a couple old Autoyre Inland mags that look like they should be thrown out, but the nubs are still good and they work perfectly. - Bob