M4A1 vertical grip, mil-spec

mil-spec P&S M4A1 and Mk18 vertical grip

Mil-Spec M4A1 vertical grip

This is made by P&S Products, who produces accessories for military weapons.  This item is identical to the Knights Armament KAC vertical grip, but is marked with the P&S CAGE code.  P&S Products, along with Colt and Knights and other manufacturers all build to DOD spec for M4A1 weapons systems.  P&S Products also makes the M4 quad RAS and the Colt M4 buttstock.

Note:  On pic depicts a KAC vertical grip for illustration.  These are 100% the same, but branded P&S Products