The ML10222 family of sights is meant to fit the 10mm and .45 ACP pistols. These are the G20,21,19,30 and 36 pistols . This set is not for the G-37 IN.45 Gap Caliber. This is a fixed set. MEPROLIGHT sights, like our other self-illuminated products & devices take maximum advantage of tritium light sources - the fail-safe, maintenance-free light sources that don’t require any external source of energy and provides up to 15 years of usable light under all weather conditions. MEPROLIGHT continues to offer the strongest guarantee in the industry for the usable light of our TRU-DOT sights.