This 64 tooth hub gear is a popular choice, paired with a 32 tooth pinion gear, to create a 2:1 ratio between holes spaced 1.5” apart. The ½” bore and 0.77” Actobotics hub pattern means you can attach a hub with the bore of your choice. The gear has a dished side and a flat side so that you can adjust the position of your gear by flipping it over.