This Access Series 2X 1.25" shorty Barlow lens is a very good, low priced import Barlow. The insert tube has a safety groove. The eyepiece receptacle uses a 3 mm thumb screw (no compression ring). This low cost Barlow is fully multi-coated, cemented, edge blackened 2 element lens system. This is a very economical way to boost power with your 1.25" eyepieces while maintaining your eyepiece's eye relief. We did not include a filter thread on our Barlows since it make much more sense to use the filter on the diagonal.