1st Knuckle for Adams Trail-A-Bikes 1998 and Older
If your Trail-A-Bike dates from 1998 (15 mm block with vertical locking pin) you will need this item to couple to a new-style hitch.
If your Trail-A-Bike dates from 1997 or earlier (12 mm block) you will also need the 15 mm-12 mm step-down block.