The Ashtabula Bottom Bracket Adaptor set (2 items per set) is an eccentric adaptor. It converts the American Ashtabula bottom bracket for use with Tongsheng mid motor upgrade kits. (Here)
The adaptor fits a bottom brackets with an internal diameter of 51.3mm. Larger diameter bottom brackets are often found on bikes with single piece cranks.
This adaptor is not internally threaded and is a press fit in to the frame bottom bracket.
For motor installation – an eccentric Ashtabula bottom bracket adaptor is required. A concentric adaptor doesn’t have enough clearance between the crank input shaft and the motor body.
This is used to convert a 51.3 mm internal diameter bottom bracket to the more common 33 – 34 mm used by mid motor kits. It’s manufactured from aluminium alloy.
Note: If you are removing a single piece crank set, as in the image, you’ll probably need a new set pedals too. Ashtabula cranks typically use pedals with a 1/2″ spindle diameter. The cranks on your motor kit will use pedals with a 9/16″ diameter left and right threaded.