Lo Pro Mag Button. Thread 4-40 Perfect Size for Most Hands. Lo Pro stands for low profile. It won't release when you lay a pistol on a flat surface or when you're shooting, because it is so low, it doesn't interfere when you don't want it to. It will, however, make it easy to release your magazine for fast reloads. Checkered face for positive look and feel. We sell a lot, so they must work.