This pack of 5 1.625"/42mm internal diameter caps allows you to protect photographic equipment with a T Ring connector. They fit over the male threads of a T Ring and fit all manner of astronomy and photographic equipment. They also fit the eye end of Vixen/Orion Lanthanum Superwide eyepieces. They are made of soft yellow plastic so they are quick to put on and take off, and easy to see in the dark.