For heavier telescopes and astrophotographic setups, an extra counterweight or two may be needed. These counterweights have an attractive finish and tri-lobe lock knob for easy grip. The 11-lb. counterweight fits the Atlas EQ-G and Sirius EQ-G GoTo mounts. Counterweight center bore measures 0.8″ (20.32mm) in diameter. Not compatible with Atlas EQ-G Counterweight Shaft Upgrade #10144.