This mirror star diagonal features a thick, oversized mirror. Polished to 1/10th wave minimum and coated with a protective, dielectric coating with 99% reflectivity. Compression ring and insert tube bevel will protect your valued eyepieces and help to better seat the diagonal in the focuser. Includes a 1.25" adapter with compression ring. Both the two inch insert tube and adapter have filter threads. Rubber grip on the 2" tube for easy handling in cold climates. Unlike most others on the market, this diagonal is made factory adjustable and this allows us to make sure it is in exact alignment before it is shipped. We adjust and then star test every dielectric diagonal we sell. This is our best diagonal available to date.