Sure Plug 1 Laser Engraved Biohazard - Designed for Gen 1-3 Glock 17, 19, 22, 23, 31, 32, 34, and 35. Aid in guiding the Magazine into the Magazine Well Flush fit to eliminate the possibility of snagging on the open cavity stops dirt and debris from entering the backstrap channel Designed for Gen 1-3 Glock 17, 19, 22, 23, 31, 32, 34, and 35. DOES NOT FIT GEN 4 Models, DOES NOT FIT 21SF Versions.