The locking ring fits to 2" barrels and is locked at the wanted position by three headless screws. Thus you can decide for yourself how much an eyepiece or adapter protrudes into the focuser or the receptacle of the star diagonal

A useful addition to this ring is a 2" extension which is screwed into the filter thread (see recommended accessories).

The 2" locking ring is often used for astrophotography. The ring prevents the adapter combination from completely disappearing into the focuser. You achieve a precise stop and determine the optimal position of the focuser.

The locking ring is also used extensively for preventing tilting problems with eyepieces with safety notch if used with compression rings. The locking ring reduces the insertion depth of the barrel.

You can also make the eyepieces parfocal to each other by using several rings, so then refocusing is not necessary anymore. Or you can set an eyepiece perfectly parfocal to a camera. Now you can locate the object with the eyepiece, focus, and then start with photography immediately by simply removing the eyepiece and attaching the camera.