This is a Glock Factory OEM, drop-free magazine for your G31, G32 or G33 pistol in .357 SIG. It is limited by Glock to only accept 10 rounds so it is compliant in states with a 10rd capacity limit. This features a hardened steel insert and is encased in high tech polymer. The polymer coating protects the magazines and prevents deformation, even when dropped from a great height. Compatible with current and previous generations of Glock pistols as well as the Polymer80 PF940 V2 80% gun frame.