The FR-4 is designed to fit the 20-spline tool fittings found on older SunTour® freewheels. Constructed from heat treated alloy tool steel, the FR-4 features a 1" tool fitting for use with an adjustable wrench, socket, or bench vise.

• Fits 20-spline tool fittings with an approximate outer diameter of 21.6 mm
• Fits Atom®, Regina®, splined Zeus®, and some Schwinn®-approved freewheels
• 1" hexagonal base can be used with 1" socket or wrench