We Recommend A Soft (70,000 Psi) Pin For Joining The Driveshaft And Drive Coupler Hub On The Flywheel On The Back Of The Engine And A Hard (170,000 Psi) Pin For Joining The Main Input Shaft To The Neck Of The Pressure Plate Flywheel. This Allows, In The Event A Pin Breaks, It Will Be The Front Pin Which Is Much Easier To Swap Out Than The One In The Rear. IH 154 Cub Lo-Boy, 185HamiltonBobs