3/4" keyseat cutter, 1/4" face width, 10 flutes.
A keyseat (Woodruff) cutter for milling keyways, slots and undercuts. It cuts 3/4" diameter with a 1/4" face width on a 1/2" shank, 2-1/4" overall.
The staggered teeth cut on the periphery, so the tool feeds sideways into an existing opening rather than plunging.