Gear 60 Tooth SOLID 3/4" ID with 1/4" key way 20PA-16DP.
Used on the Final output shaft of the 16.07 to 1 gear reduction box.
http://www.staton-inc.com/store/products/1_Output_Shaft_16_07_to_1_reduction_gearbox_for_Vertical_Shaft_Engines_Post_Hole_Auger_Drill_Water_Wells-1200-39.html
The gear are Heat Treated and broached with a extra wide 1/4" key way.
Most 3/4" shafts will use a 3/16" key.
You could use a 3/16" x 1/4" off set key if needed.