Para Ordnance Magazine Base Pad
Originally designed for competition shooters, this removable nylon base pad gives increased durability to the magazine, while providing an extended look and feel. The 2-piece base pad does not increase the magazine's overall capacity. Fits most Para Ordnance and Para USA double stack magazines. The bottom of the base pad is marked with the numbers 1 through 10. This allows the shooter to indicate the number sequence of their magazines.
This part is found in the following schematics