Top Tube Adaptor

A top tube adaptor contains: a body, two fixers, and a slidable rod. The body includes at least one slot, and a respective positioning rack has multiple teeth. The slidable rod includes a channel and a locking seat for accommodating a rotatable connector. The rotatable connector includes two shafts, a press portion, a button, an orientation segment, an engagement portion, and a first resilient element. A respective fixer includes a curved hook, a cutout, two tabs, a coupling projection, a column, and a second resilient element. The second resilient element has two abutting segments, one of the two abutting segments abuts against the two tabs, and the other abutting segment contacts with or removes from the coupling projection so as to close or open the cutout. The two fixers are connected with two ends of the slidable rod respectively.