The Alpine Astronomical Baader 2" SCT Female to M48i Female Zero-Length Reducing Adapter was originally designed to allow the use of their Hyperion Universal Zoom Mark IV eyepiece with any photographic M48x0.75 threads. Since it is just a simple reducer ring that fits standard 2" Schmidt-Cassegrain Telescope (SCT) threads, it can be used for a variety of applications beyond its initial intended purpose as either a general-purpose reducer or expander based on your needs, for example, as an expansion ring that converts a photographic M48-thread into a male 2" SCT thread.
The outside male threads match the Hyperion locking ring as well as standard 2" SCT visual back threads, and the inside female threads are M48x0.75 size. With continuous threads, when it is installed on your Hyperion eyepiece, SCT backs, and other 2" threaded accessories, the adapter can be set flush, so while the thread size is converted there is no additional optical length added that will affect back focus distances. To assist in proper installation and removal, the ring has two 2mm face holes that allow the use of their Spanner Wrench, which is available separately.