Making your own 2" eyepiece just got a lot easier! These screw in on top of all of our 2" threaded barrels. 45mm diameter bore (opening) fully threaded. Comes with two threaded rings to hold your lenses in securely (others also available separately). One is 40mm opening and is 36mm long (will fit 37-39.5mm lenses) and the other has a 28.5mm opening and is 25mm long (will fit lenses 25mm to 28mm diameter). Some of our already mounted achromats (L3719 for example) fit inside the universal eyepiece lens holder well and can be tightened with a M2814D (Inside the 2" barrel). Each universal adapter is new and comes with a 2" x 1-3/4" long threaded barrel attached.