This is an original Singer (SIMANCO) C-Clamp used with the Singer Hand Crank Pinker as well as the Singer Sewhandy Model 20 Child's Sewing Machine.
A C-Clamp is of necessity for the Pinker and Sewhandy to work properly because it needs to be securely fastened to a table for the crank to turn freely without the pinker and machine shifting. If you have a thicker table or surface than the original c-clamp allows, most any new hardware c-clamps will work - just use a larger size (found at most hardware stores).
For more information about this and other Pinking tools we have look under the tutorial tab.