Thread Size: 5/16-24 Superior vibration dampening and wind performance. Almost no sag even when loaded with a large number of weights. Aerodynamic design with ring grooves giving superior X and Y axis vibration dampening. - Superior vibration dampening in all axes...X, Y, Z - Equally spaced ribs around the circumference for superior Z-axis vibration reduction - Arc-shaped scalloped rings with the smallest diameter grooves in the middle for superior x-axis and y-axis vibration reduction - Strong proprietary rubber