Briggs & Stratton 8.50 TP Professional Series Engine 7/8" x 3-5/32" Vertical Shaft #121S02-2015 (121R02-0110) Briggs 8.50 TP Professional Series Shaft Dimensions 7/8" x 3-5/32" shaft, tapped 3/8"-24 with 3/16" keyway. Ready Start, no choke- no priming. Fixed speed throttle design. 2 year consumer/ 1 year commercial warranty.