The diagonal uses a non-marring molded compression ring to hold the eyepiece in place, rather than a set screw that can scratch the barrels of your eyepieces. The compression ring is tightened by a ribbed thread-on collet around the eyepiece holder. Rotate the collet in one direction and the compression ring tightens on the eyepiece to hold it firmly in place. A simple twist on the collet in the opposite direction loosens the compression ring’s grip on the eyepiece. With a collet, instead of a thumbscrew as most diagonals use, there is no chance of losing the thumbscrew in the dark (along with the ability to hold your eyepieces safely in your diagonal).