Ridgeway made these in standardised shank sizes, and¼″ is the smallest common one. Ridgeway often didn’t stamp the size on their smaller centre bits — especially the early ones. pre‑Jennings auger systems.
Archives
Vintage 10.1 mm Auger Bit Sheffield England No. 6 8.5″ Long tapered square shank
Shank is stamped“6”, indicating the size in the Ridgway numbering system. Markings: Size“6” stamped on shank.