Biastro & jring. Yall's info has been very helpful - I appreciate it! I found a pic of the Tasco 6651 20-45X eyepiece. See attached. My Tasco 25T appears to be simply a rebranded Opticron, as both scopes appear to have the exact same exterior shape.
I am almost certain that an Opticron zoom eyepiece will attach to some short secondary male threads that are concentric above the main threaded hole for fixed eyepieces. On my scope, these secondary male threads have an OD of 1.375" or 34.93mm.
Based on that, do you tend to agree about Tasco's / Opticron's compatibility? Thanks again.