This is C- Mount adapter with M38 port(One end is for C-mount(CS-mount) (25mm), the other end is 38mm for most microscope trinocular port.
This adapter is for c-mount camera assemble
The C mount adapter is design for Camera sensor size: 1/2.5", 1/2.8", 1/3" / 1/2" inch
Magnification(optional): 1X , 0.5X , 0.35X
1X: standard working distance, standard magnificaiton.
0.5X: Large working distance, less magnification
0.35X: Largest wroking distance, least magnification