I'm going to add pictures from my phone, but I'm typing this out now,
I was able to sort of line things up to a point of reference. Also I have a Roman's MPP clamp and multiple kinds of T track to measure as well.
The mystery part and MPP lever are 7mm high
Mystery part is also around 7mm wid
The MPP sidebar face is about 10mm or 1cm
The T track is 18mm wide, roughly. (I have Gino track as an example and it matches)
little brass screw heads are 4mm
The bored holes on the barbican are
13.5mm top to bottom (the wide part of the oval)
and I'm getting
10-11mm for the caps
I have vintage
M5 Oxide bolts that are 11-12mm across the face
I'm 90% sure the ROTJ Vader Gx has M5s (right
Sym-Cha ?) and I thought the pipe stunt had the same size, but there's not much to compare it to on that saber.
Checked the severed hand picture and I'm getting
11-12mm for the one visible bolt.