Knurled Knob Swivel Screw Clamp With Large Pad – 5/16-18 Thread X 1-31/32. For Use When Finger Tightening Provides Adequate Pressure. Pad Can Be Detached From Stem Via A Left Hand Thread. When Using, Thread Stem Through Hole, Then Screw Pad Onto Stem On Other Side Of Hole. Pad Makes Maximum Contact With Angled Of Uneven Surfaces. When Pad Comes Into Contact With Part Or Workpiece, It Stops Rotating And Thus Prevents Marring. Black Oxide Finish.