Unfortunately, most t-rings are backordered, but I found two sources that seem to have them in stock (Amazon & Orion). They appear to be the same product, so I want to make sure that I am ordering the correct item.
After reading the following text of the reducer/flattener description, it seems that I am on the right track, but correct me if needed.
The Astro-Tech ATRF60 reducer/flattener threads on the 60ED focusers. The flattener is threaded for attachment to the telescope via a 54mm metric thread. The camera side of the reducer has 48mm T-threads to connect to a T-ring and camera body. Back focus is 55mm from the shoulder of the reducer to the image plane, the standard spacing for 35mm and DSLR camera bodies.
Edited by nickkohrn, 22 April 2021 - 09:40 AM.