For heavy duty clamping
PART # THREAD A B C D R20-SDC 1/4"-20 3.50" 3.0" 1.0" 1.0" R20-LDC 1/4"-20 5.25" 3.0" 2.0" 1.50"
PART # THREAD A B C D R8-SDC M8 89mm 76mm 25mm 25mm R8-LDC M8 133mm 76mm 50mm 38mm