Abstract: A multi-part form for casting concrete structural units having spaced parallel and vertical sidewalls and horizontally spaced parallel and lateral connecting arms therebetween, the connecting arms having mortises at the bottom and tendons at the top. A stationary base and support means has upwardly exposed surfaces for forming the bottoms of the sidewalls and the arms and a core means thereon forms inner vertical surfaces of the arms and portions of inner vertical surfaces of the sidewalls of the structural unit. Opposing movable sidewall form members form outer surfaces of the sidewalls and opposed movable arm and sidewall form members form outer surfaces of the arms and inner surfaces of the sidewalls outwardly of the arms. Sidewall end surface form members on the sidewall form members form the end surfaces of the arms. Tie and strip bolts respectively secure the movable form members in inner assembled positions and urge the members outwardly in a stripping operation after casting.