It is the transition / reduction coupler of the Barcoup system. The rebars especially in the high-rise constructions make transitions from large to small diameter statically. This type of coupler is used in the rebars where the transition is made. For example, in the Q32/Q25 transition coupler, the gear is chased on one side of the rebar according to the heading parallel gear system for Q32 and on the other side of the rebar according to the heading parallel gear system for Q25. The rebar is screwed with a specially-designed coupler and the mounting is completed.

1 rebar with short gear – Large diameter
1 rebar with short gear – Small diameter
1 plastic protective plug
1 reduction coupler