Confused about how this works?

[jjphoto93]

I'm pretty new to mf lenses and in particular lens repairs. I recently picked up a cheap Jena 28mm f2.8 (I believe it's the same as the Praktica design) on ebay in order to clean it up/practice disassembly. I've managed to strip and clean everything, declick the aperture and regrease the helicoid but I can't work out how the front section fits onto the rest of the lens. This part came off while I was unscrewing the front element initially, so I have no idea how it fitted originally and there doesn't seem to be any threads/way to push fit it onto the helicoid whilst reassembling it. Am I missing something obvious?

[Eddie46]

Can we see the parts you have left so far?

[Lightshow]

Please post a few more pictures of each part, from different angles.
Also with the helicoid extended.
This front part, did you reassemble any part of it? this is exactly how it came off?
I'm thinking the threads that mate to the silver helicoid/aperture block have retracted into the front group, it may have to come apart so as to go back together in the correct order, not as a whole unit, I suspect it somehow came apart as a unit when it wouldn't normally come apart like that.

[jjphoto93]

Thanks for the ideas! Turns out the threads had spun into the front section which was confusing me. All fixed and put back together! Thanks guys

[Lightshow]

Glad you figured it out.
Cheers.