The outside measurements are 3/4" diameter and

Universal tab mounts and a shallow tunnel make for easy mounting on your backbone

and the pictures do not lie

T120/TR6 1963-1972

These are really sturdy

Radius Steering Stem Bolt - Chrome - 39mm Narrow Glide Front End Gas Cap Type_Harley Thread-In The outside measurements are 3/4"The stock steering stem bolt looks suited for building a swing set, replace it with this precision machined, steel Radius Stem Bolt from Lowbrow Customs. The square broach accepts any standard 3 8" drive ratchet for easy install. Available in your choice of chrome or black electroplate, pair with the Radius Fork Tube Caps for optimum style. For your 39mm narrow glide front end. Made in the USA. See Additional Information below for fitment.