Quill-return spring for Fobco 7-Eight and 10-Eight models - the maker's original specification, UK-made part. Not to be confused with the thiner, fewer-coil and inferior type sometimes advertised on ebay.   The spring is 0.75 inches deep (19 mm) by 2.45 inches (62 mm) in diameter over the coils.
Details of the spring for the smaller Fobco "Star" drill are here.