This factory Glock OEM Backstrap/Beavertail Set (MPN 30819) uses the Glock Modular Back Strap (MBS) System, letting shooters fine-tune grip size and rear-grip-safety engagement to match their hand for a more comfortable, controlled hold. The kit includes backstrap panels in two standard and two beavertail profiles/sizes plus a retention pin, giving a factory-correct custom grip fit without gunsmithing.