Majestic Arms discovered a problem with the design of the new Ruger Mark IV pistol, and the new Majestic Arms Ruger Mk IV Bank Vault Locking Block solves the issue. The Majestic Arms Ruger Mk IV Bank Vault Locking Block works by eliminating the issue with a rubber plug found behind the pivoting bar that attaches the upper and lower receiver. The locking block adds an adjustable steel piece to the assembly. Designed to enhance accuracy Removes any play from the hinge Locks up any movement between upper and lower. The Majestic Arms Ruger Mk IV Bank Vault Locking Block removes any chance that the deterioration of that rubber plug will degrade pistol accuracy. Mfg: Majestic Arms, Ltd.