Orion 7384 7.5lb Counterweight for SkyView Pro and AstroView Perfect for using a larger telescope optical tube on a SkyView Pro or AstroView mount Lock knob has a nylon tip to avoid scratching your mount counterweight shaft Extra 7.5-lb. counterweight for balancing heavy loads on Orion SkyView Pro EQ or AstroView EQ equatorial mounts Features an attractive finish and a large lock knob for easy grip, even with gloves on Hole diameter is at 0.795 inches (20mm)