1" keyseat cutter, 3/16" face width, 12 flutes.
A keyseat (Woodruff) cutter for milling keyways, slots and undercuts. It cuts 1" diameter with a 3/16" face width on a 1/2" shank, 2-3/16" overall.
The staggered teeth cut on the periphery, so the tool feeds sideways into an existing opening rather than plunging.