Abstract: A holder for a right triangular speed square, having a transverse flange extending along one side, includes a pair of side panels disposed in spaced, parallel relation which define a hollow interior having front, rear and bottom openings in the form of elongated slots. An inclined rear wall connects the side panels and separates the rear and bottom openings. Apertures in the side panels cooperate with rivets to secure the holder to a carpenter's apron. The rear wall abuts a side of the speed square forming the hypotenuse. An elongated, rectangular tubular portion formed along top edges of the side panels possesses a floor with a central opening communicating with the hollow interior portion and defining aligned, opposed, spaced ledge members which abut the transverse flange. A pair of upstanding tabs disposed on the ledge members adjacent the front opening, on opposite sides of the central opening, engage a leading edge of the transverse flange.