Infinity bushings and T-bushings are designed to adapt larger-bore shaper cutters to smaller spindles. These T-Bushings feature a top and bottom "T" with a straight piece in the middle for when you have a taller cutter stack. These T-Bushings all have an 1-1/4" Outside Diameter (O.D.)
Item BUS-108 is specifically designed for Infinity Tools Insert Pro Interior & Exterior Door Making sets, found here.