I need to disassemble THRU attenuator like this
How can I do that?
There should be a circlip retaining the collar. Collar is the freely rotating part on the right. The circlip or some other circular spring will be buried in the gap between the collar and the shield tube. Once you remove the collar, I imagine the next steps will be more apparent.
Disclaimer: I have never disassembled one exactly like what you show, but that's where I'd start.