Orion 7374 144mm ID Telescope Tube Rings Set of two cast-aluminum rings with quick-release, hinged clamp knobs and felt lining One ring has 1/4"-20 piggyback camera adapter; the other has threaded 1/4"-20 hole Sold in sets of two rings. Mounting bolts and washers are included Use with 127mm Mak-Cassegrain 0