Clear 2″ and 3″ Tri-Clover Clear Caps. As of this posting, Brewers Hardware has these on clearance. $2 for the 2″ size and $5 for the 3″ size. Availability is limited, check Brewers Hardware’s Clearance Page for current availability, selection and pricing.
Also: Brewers Hardware has a gigantic selection of Tri-Clover Compatible Fittings including some really unique offerings