Brass thumbscrew with nickel plating.
I have never seen steel shrouds even I have had 3 mpps in my hands.
However I didn't see any thick mpp shroud like the one used on the original prop, you can see it's closer to a parks replica than any genuine shroud I have seen for now.
About the number, some have, other have no number, and sometimes it's not under the shroud.
Maybe your clamp is for a different fixation, I know there are at least two different sizes of standarts clamps, the narrow, quite similar to graflex, and the large one, larger than graflex, a bubble doesn't fit inside.
I have never seen steel shrouds even I have had 3 mpps in my hands.
However I didn't see any thick mpp shroud like the one used on the original prop, you can see it's closer to a parks replica than any genuine shroud I have seen for now.
About the number, some have, other have no number, and sometimes it's not under the shroud.
Maybe your clamp is for a different fixation, I know there are at least two different sizes of standarts clamps, the narrow, quite similar to graflex, and the large one, larger than graflex, a bubble doesn't fit inside.