This is a machined billet aluminum cap with knurled edge. Single cap (or right side cap) is vented. Your stock HD rubber gasket (HD 61100194) will fit these caps, or they can be supplied with the HD rubber gasket as pictured. (Yes, the gasket does add $20 to the price for EACH gasket - blame Harley, not us) . Available with or without weld-in steel bung(s).