Abstract: The present invention is related to a new bicycle frame tube coupling structure and, more particularly, to a tight coupling which includes a pair of solid lugs having large curved front edges fixedly connected to the wall surface of the tight coupling through a silver brazing process. When a locking bolt is inserted through the pair of lugs and screwed tight, the solid body of the two opposite lugs and the two large curved surfaces provide an increased pressure onto a fixed tube to firmly tighten a movable tube, which is contained in the fixed tube and both of which are set in the tight coupling, so that the movable tube be firmly positioned therein.

Abstract: This invention provides an improved adjustable tube clamping connector, especially one used for making adjustable connection of an inner tube and outer tube as required by the actual conditions. The outer tube has an open slot and is attached by welding to a clamp with two lugs on the slot. Fitted in the cavities of the lugs are a pair of clamping pieces each of which has a pair of extensions with curved surfaces. With the back of the clamp pieces against the bottom of the cavities of the lugs and the curved surfaces of the extensions on the external surface of the outer tube, they will give added strength and pressure to make the outer tube firmly grip and hold the inner tube so as to bear greater load and to ensure safe use.