The ball base designed to fit into the cylindrical or hexagonal bore wall of motorcycle fork stems. Suitable for stem tube holes 12mm to 25.4mm in diameter Package comes with two sizes of metal spacers. Small size spacer fit for tube 12mm to 18.5mm in diameter, Large size spacer fit for tube 18.5mm to 25.4mm in diameter. You can choose one size of the spacers according to the tube diameter for installation. It is not supported to use two spacers of different size at the same time The metal motorcycle fork stem base included B size 1" TPU ball allows for connection to RAM MOUNTS & BRCOVAN any B size double socket arm PRE-INSTALL CHECK: Measure tube diameter, select and fit the correct spacer before installing the ball base. Support minimum tube depth 38mm ANTI-THEFT DESIGN: The bolt head of the fork stem ball base has a specially designed screw groove, and the package comes with a special wrench for tightening or loosening the bolt. Adds extra security to equipment att