1 1/8 in - Threadless

20" x 4 Fat Tire Fork Details: CDHPOWER 20"x4.0" Fat Bike Snow Fork Fat Bicycle Fork. Durable Construction: Built with an aircraft-grade aluminum body and high-strength steel stanchions, this front suspension fork can withstand heavy off-road use.Travel: 170mm Spread: 135mm Smooth Riding Performance: Air suspension damping absorb bumps and vibrations for a comfortable ride over rough terrain, ensure reliable handling on trails and hills.Required for 11/8" Headset ThreadlessEasy Adjustability: The manual lockout lets you stiffen the fork for paved sections or free it for more suspension over obstacles.PLEASE NOTE1: the best safe speed if racing: 35km/h；Outside Diameter of Up Tube: 32mm/1.26inch and 43mm/1.693 inch for lower legDouble Shoulder20"* 4.0" Fat Tire Air Suspension Fork with 1-1/8" Headset ComboManual Lockout, Air suspension damping.Outside Diameter of Up Tube: 32mm/1.26inch and 42mm/1.693 inch for lower legDisc brake bracket( center hole to center hole: 75mm) ;compatible with 20"*4 inch tire maxTravel: 170mm Spread: 135mmPLEASE NOTE1: the best safe speed if racing: 35km/h； 26" x 4 Fat Tire Fork Details: CDHPOWER 26" Suspension Fork 4.0" Fat Bike Snow Fork Fat Bicycle Fork. Triple Tree Suspension Fork with Double BLACK Shoulder. Durable Construction: Built with an aircraft-grade aluminum body and high-strength steel stanchions, this front suspension fork can withstand heavy off-road use.Fork is compatible with cdhpower gas tank frames. Smooth Riding Performance: Air suspension damping absorb bumps and vibrations for a comfortable ride over rough terrain, ensure reliable handling on trails and hills.Travel: 150mm and Spread: 135mm; Required for 11/8" Headset ThreadlessEasy Adjustability: The manual lockout lets you stiffen the fork for paved sections or free it for more suspension over obstacles.PLEASE NOTE1: the best safe speed if racing: 35km/h；Outside Diameter of Up Tube: 32mm/1.26inch and 43mm/1.693 inch for lower legDouble Shoulder26"* 4.0" Fat Tire Air Suspension Fork with 1-1/8" Headset ComboManual Lockout, Air suspension damping.Outside Diameter of Up Tube: 32mm/1.26inch and 42mm/1.693 inch for lower legDisc brake bracket( center hole to center hole: 75mm) ;compatible with 26"*4 inch tire maxTravel: 150mm Spread: 135mmPLEASE NOTE1: the best safe speed if racing: 35km/h； ReferenceAir Suspensionshoulder manual control260mm length1 1/8" Threadless HeadtubeDisc brake bracket( center hole to center hole: 75mm)The air pump valve for the forkQR: 135*9mm