First, let me just say I don't have any newtonion reflectors, so I'm not sure how things attach to the focuser.
But when I talk about a 2" focuser, I'm referring to a focus tube that accepts a 2" nosepiece, and uses one or more thumbscrews to hold it in. A 2" nosepiece can be the bottom end of a 2" eyepiece, the front end of a 2" diagonal, or a 2" nosepiece that is part of a T adapter arrangement. So when you mention "screwing onto a 2" focuser", I'm not sure what you mean. My undertanding of a 2" focuser is that you insert 2" attachments, not screw anything onto it.
The only piece I recongnize in your photo is the part on the right. That appears to be a T-ring which attaches to a DSLR on one side, and has a female T-thread (?) on the other. I can't really see the other side so I don't know for sure.
The part on the left might be part of a 2" focuser. The top of it looks like it might accept 2" attachments like and eyepiece, diagonal, etc. But I'm not sure what the bottom attaches to. Perhaps it attaches to a focuser mechanism on a scope, which is why I'd think of it as possibly part of a 2" focuser.
I'm not sure what the middle piece is.
But again, what I think of as a normal arrangement would be, from camera to scope:
2) T-ring (camera mount on one side, female T-thread on the other)
3) Male T-thread to 2" nosepiece adapter. Example: http://agenaastro.co...pter-ff145.html
4) 2" Filter - screws into the end of the 2" nosepiece
5) 2" focuser tube (accepts 2" nosepiece)