Trapezoidal Tap, Tandem Acme Tap High speed steel,ground thread. Size: 1/4" to 2". TRAPEZOIDAL THREAD TAPTrapezoidal screw threads were devised to allow rotary and transversing motion on machines; and are also used in jacks, valves, presses and other mechanisms where heavy loads are encountered. The trapezoidal thread is characterized by a 30° included angle. Trapezoidal taps typically require ...