Almost the same size as the old Head Mate. However, installation is going slow. Different bolt pattern for the base - new holes are easy, but what to do with the old ones? Hose for the flush water is completely different - Head Mate came into the back over the joker valve. PHC wants the flush water to come into the front from below. Tomorrow I'll have to reroute the flush water line - don't really want to break off the inlet nipple to the control valve! Discharge hose hooks up fine - actually used it to locate the head!