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[rmorein]

This finder scope has a helical focuser, a miniature version of the helical focuser of the 80mm F15. Rotating the focus collar, the eyepiece tube extends from the focuser body. The eyepiece tube ends in what appears to be a 30mm  internal thread, into which threads a machined aluminum 0.965" eyepiece holder, complete with setscrew.

 

The mystery I am inquiring about is the origin of the 30mm thread. Is it "standard anything"?

Edited by rmorein, 20 February 2025 - 08:49 PM.

[YourNotSirius]

This finder scope has a helical focuser, a miniature version of the helical focuser of the 80mm F15. Rotating the focus collar, the eyepiece tube extends from the focuser body. The eyepiece tube ends in what appears to be a 30mm  internal thread, into which threads a machined aluminum 0.965" eyepiece holder, complete with setscrew.

 

The mystery I am inquiring about is the origin of the 30mm thread. Is it "standard anything"?

Photos would always help but, also knowing when it was made and by who, could determine the pitch of the threads.

 

The easiest thing to do is get a thread pitch gauge and measure the threads. It is about 99-44/100s certain to be metric. Harbor Freight and better hardware stores have those gauges and they are not expensive. If you know anyone who is a machinist they should have several of them.

 

FWIW

 

Q