The GLOCK Modular Back Strap System enables the pistol to adapt to an individual shooter's hand size. Installing and removing the back straps is a simple procedure and adding or removing a back strap does not change the grip angle of the pistol. The smallest back strap is integrated in the GLOCK MBS frame reducing the trigger distance of the standard size frame by approximately .08 in. The medium back strap adds approximately .08 in – equaling the size of a standard frame – and the large back strap increases trigger distance by a total of approximately .16 in. Models: G17 Gen4, G17 Gen5, G22 Gen4, G31 Gen4, G34 Gen4, G34 Gen5, G35 Gen4, G37 Gen4 (includes MOS)