Adapter for attaching 31.7mm American size eyepieces to 2" eyepieces CNC Cutting + Black Anodized for a Robust and Beautiful Finish The eyepiece is held in place with a collet chuck that rotates tightening. Tightens the eyepiece barrels evenly from the perimeter for a very secure hold and ensures constant centering. The 2" barrel has a straight type that does not snag when putting on or taking off. The barrel tip is also equipped with a 48mm filter thread. This adapter is very useful when installing heavy eyepieces, especially in situations where centering is critical for optical axis correction.