Abstract: A coupler structure which facilitates the internal joining of a first length of hollow plastic pipe having internal corrugations defined by a plurality of alternating peaks and valleys to a second length of similar pipe or to some other structure. The coupler is molded from plastic to have at least one cylindrical end portion dimensioned for longitudinal receipt in the second length of tubing or other structure which is to be coupled to the first length. This one end portion includes a plurality of integrally molded cleats extending generally radially outward thereof. The cleats are selectively movable between first locking positions for lockingly engaging the second tubing length valleys and second non-locking positions which permits forced insertion of the coupler one end portion into the second tubing length. The cleats are hinged to the one end portion generally laterally thereof and are continuously urged toward the first position by the resilient nature of the plastic construction.