Shift Assist is a needle thrust bearing
Gives you smoother upshift and backshift by eliminating spring bind and allowing the moveable to rotate freely
This thrust bearing replaces the 0648-453 plastic washer that the spring rides against, #7 in the diagram shown in the last picture
Dimensions are about 2.56″ OD, 1.75″ ID, and 0.15″ thick
This includes the shift assist thrust bearing only
BDX PART # 50054
D&D RACING PART # 200-0042