The Singer 301 was designed to be both cabinet mounted and portable. Unlike the full-size Singers before and after it, it does not have the slots and set screws to mount the machine directly to the cabinet.
The Singer cabinets for the 301 came with this cradle setup which does mount to the two swivel studs on the cabinet. The 301 simply clips into this cradle. It is removed by pressing down on the spring loaded lever.
This is a really great way to mount a Singer 301 in a cabinet!
Comes complete with the swivel studs, and the receiving tabs that hold up the operator side of the cradle and machine.