Orion 7371 100mm ID Telescope Tube Rings Set of two 100mm inside diameter cast-aluminum telescope tube rings with quick-release, hinged clamp knobs and felt lining One ring has 1/4"-20 piggyback camera adapter; the other tube ring has a threaded 1/4"-20 hole Sold in sets of two telescope tube rings with mounting bolts included Use with any Orion equatorial or altazimuth telescope mount - use with some mounts may require a tube ring mounting plate (sold separately) Inside diameter of each tube ring is 100mm - works with 100mm diameter telescope optical tubes