1/4 3/8 UNC Metal Adjustable Clamping Thumb Screw Wing Knob Lever Hand Grip Bolt
1/4-20 UNC, 3/8-16 UNC （Unified National Coarse Thread）. - Thread Size: 1/4-20 UNC or 3/8-16 UNC. Adjustable knob screw is spring loaded which can be pulled out or turned to a more friendly position after being tightened.