This is a clamping adapter that allows you to provide a male T2 thread on the end of any suitabley sized eyepiece that does not feature a thread. The adapter features an internal compression clamp that is rubber coated to prevent scratching of the eyepiece barrel.
The internal depth of the D59 clamping adapter is 20mm with an initial 5mm gap before the start of the compression ring. The internal diameter allows it to be fitted on to eyepiece barrels up to 59mm in diameter. Included with the clamping adapter are some self adhesive rubber strips in 1,2 and 3mm thickness. These can be inserted inside the clamp to pack it out allowing its use with barrel sizes down to as little as 50mm diameter.
This clamp allows you to use any suitabley sized eyepiece for digiscope or projection photography, night vision eyepieces and also optical testing on artificial stars.
While this may seem like a large adapter that you would not normally need, it is well suited to long focal length of super wide angle eyepieces that do not have thread adapters as standard.