Originally Posted by
fietsbob
The bottom of the hinge is a quill, that goes inside the fork, that is the interface between the 2..
I'd use that I.D.
The Dahon Radius are similar to threadless, the stem clamps to the OD of the fork, but instead of a star fangled nut the ID of the for is threaded and there is a large stubby bolt that draws down on the stem and sets the bearing load.