Short Adapter Shank #77 is the shortened version of Standard Adapter Shank #75. Serving as a connecting piece between needle bar and accessory, Short Adapter Shank #77 allows other manufacturers’ presser feet to be used on BERNINA machines.
If these feet are short-shanked, they won’t fit on the machine’s standard holder without an adapter. By contrast, Standard Adapter Shank #75 is used e.g. with BERNINA sewing accessories such as Ruffler attachment #86.