This Taran Tactical Innovations GLOCK base pad works on GLOCK models 21/41. This TTI base pad will add 4 extra rounds of .45 ACP to the magazine. This base pad does adds a little extra weight to the magazine which helps the empty mag drop free easier for faster reloads. This TTI GLOCK base pad, just like all TTI base pads, is designed to give you the edge over your adversaries. TTI uses a patented push pin design to lock the base pad to the magazine, which makes for easy field stripping and cleaning your magazines between stages. Just push down the pin, slide the base pad on and push the pin up to lock the base pad onto the magazine. Their one piece design is great because there are no extra parts or tools needed to attach the base pad to your magazine. The base pad itself is machined out of billet aluminum and is hard anodized to ensure durable long lasting color. All machining and manufacturing is done in the USA.