T 2 external thread on the accessory side; safety groove to stop lens falling out
The light path is extended by only 3 mm; which is good news for the focus position as it is hardly changed
2 inch diameter T 2 focal adapter; fits into all 2 inch focusers
The extension tube has a M48x0.75 interior thread and a M48x0.75 exterior thread for elegantly solving spacing problems in astrophotography
The required spacing can be achieved by combining several extenders of differing lengths; you can use 1 piece; 2 pieces; 3 pieces or 4 pieces of the extension rings as you like