1/2" keyseat cutter, 3/32" face width, 10 flutes.
A keyseat (Woodruff) cutter for milling keyways, slots and undercuts. It cuts 1/2" diameter with a 3/32" face width on a 1/2" shank, 2-3/32" overall.
The staggered teeth cut on the periphery, so the tool feeds sideways into an existing opening rather than plunging.