AstroISOmetric AstroISOmetric mm 60 3 25.4 C-mount C-mount 0.79375 external 6g 25.308 24.8349 24.4415 internal 6H 25.5291 24.9879 24.6831 24.65 external 4g6g 25.308 24.8554 24.462 28.5 1.25 inch filter 1.25 inch filter 0.6 external 6g 28.427 28.2352 27.848 internal 6H 28.5961 28.2352 28.0287 28 external 4g6g 28.427 28.1267 27.8645 42 M42x0.75 M42x0.75 0.75 external 6g 41.908 41.4409 41.0475 internal 6H 42.1201 41.5789 41.2831 41.25 external 4g6g 41.908 41.4594 41.066 48 2 inch filter thread 2 inch filter thread 0.75 external 6g 47.908 47.4409 47.0475 internal 6H 48.1201 47.5789 47.2831 47.25 external 4g6g 47.908 47.4594 47.066