Abstract: Forming a joint in a thermoplastic strip by cutting a V-shaped notch in the strip, arranging a thin, heated blade within the notch and bending the strip about the apex of the notch for compressing the walls defining the notch against the blade for heating such walls, and then removing the blade and continuing the bending until the walls contact and join together. The notched strip is inserted between a pair of movable compression jaws, and the blade is mounted for reciprocating movement between and outwardly of the jaws. Positioning and holding means are provided for locating and holding the strip during the steps of forming the joint between the jaws.