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Good summary of common astronomy threads.
Filter Connections
2″ filters use:
Male M48 x 0.75 thread
1.25″ filters use:
Male M28.5 x 0.6
T Connection
Male T/T2 thread (M42x0.75)
ZWO cameras
ZWO has standardized their connections. They use a T/T2 M42 x 0.75 thread. Therefore you can attach either a 1.25″ or 2″ nose adapter to the camera that uses a T/T2 male thread.
Eyepiece Filters
These filters fit on the back of the eyepiece. For a 1.25″ filter, they commonly use an M28.5 x 0.6 thread.
1.25″ Filter Wheel