This is a X-GRIP known as the Mag Spacer, model 1911M380.
The 1 piece XGRIP snaps over the 7 round metal floorplate. No tools are required. Once installed" the XGRIP protects the extended magazine and floorplate. Compatible with Colt MUSTANG or SIG SAUER P238 .380 cal 7 round metal floorplate magazines.
Features:
Improved Comfort, Control, and Accuracy
Protects Extended Magazine
Secure Fit