Z355E Warning: Does NOT Fit Older Z355E Units (serial number BEFORE 060000). Direct Replacement For ALL Units 060001 and later. High Torque Coil: This OEM Upgrade is 150ftlbs of Torque (OEM is 105 ftlbs). Higher Torque Means this Clutch holds Strong Even in the Toughest Cuts and Prevents Overheating caused by slippage. BIGBearing: The Pulley Bearing Takes a lot of abuse and is often the first thing to fail. We use a Larger Pulley Bearing for a much longer life. We also designed our Billet Pulley with a snapring making the bearing replaceable. Tough Billet Pulleys: Billet Pulleys Reduce Belt Wear and Maintain Perfect Blade Speed. Our Billet Pulley Design uses a Snap Ring and Allows for Bearing Replacement. Premium C3 Bearings: To Combat Heat HD Designed and Spec’d these bearings with C3 Clearances, Premium High Temperature Grease and on Most Models a Larger Tougher Bearing. Cool Coil Technology: We use a Proprietary Composite Material Instead of Plastic. This Allows the heat to Escape the Clutch Faster. Less Heat = Longer Life HD Clutches are designed at HD Clutch and Assembled in the USA. Higher Torque: 150 ft-lbs (OEM is 105). We add a few more windings to our coils to provide the maximum gripping strength to prevent damaging micro-slipping during tough cutting conditions. The HD Switch BIGBearing design addresses the #1 reason clutches fail with a larger tougher pulley bearing. Machined Billet Pulleys: It is easy to damage formed pulley and damage (even a small stone nick) damages the belt with every rotation. With our Billet Pulley design, we include a snap ring so the bearing is replaceable, making this clutch rebuildable. Clutches all run very hot; we use a composite material instead of plastic to allow the heat to dissipate much faster. This makes the HD Clutch run much cooler; extending the bearing and clutch life. HD Clutch wrote the Bearing specifications to include Premium C3 Rated Bearings and high temperature rated synthetic grease to combat heat. Less Heat = Extended Life.