These are the original one and only in ~1995/6 did they, I think, move to riveted version. Not sure how you missed this style out. M737 on the other where the same just silver and always riveted together.
So are the most common type.
Now the machine screws are very hard to get out, unless new. They round off easily.
The mini crank bolt parts come loose and end up 'somewhere'
I still have a few of these with loose top rings etc..
The larger p-type (12-32) is just the same.
P.S. I could well be wrong on the switch to riveted, I only remember the bolt/screw type and only bought these before loosing interest in late 1995, turn of 1996.
The M900-I had come out and was riveted, these are IG style cassettes and you see the extra profiling on the back f the cogs for down shifts.
I had long since moved to M737 as they where cheaper, weighed the same and where exactly the same design so performed the same other than the lack of screws and bolts that made your m900 disintegrate.