NDZ Grip Frame Slug Plug P4 for Glock Gen 1-3 G Model 21 Engraved NDZ P4 Grip Plug for GLOCK 20SF 21SF GEN 1-3 ONLY 1000+ High Resolution Permanent Laser engraved images, will not rub off, not painted, custom engraving too - by NDZ Performance Fits flush, prevents snagging Quick install using a tight friction fit Helps guide mag. into mag well.