AXCEL® AVX Ring Pin and Rheostat Cover Combo For AVX-31 or AVX-41 SCOPES Ring Pin: Patented technology for quick interchangeability of ring pins. Choose: .010" or .019" Fiber in Green, Red, Yellow, or Blue Rheostat Cover: Cover for Ring Pin to eliminate pin starburst or allow for extra lighting to hit fiber optic based on sun angle or location and varying brightness situations.