This likely belongs in "Hardware, setup and repair" not Luthier's corner.
Probably 1.5mm
The 170 manual doesn't offer much help, as it lumps them into a "bridge assembly"
The 270 manual admits that the screws are "3.0 x 12" and "3.0 x 14"
I'm guessing that they mean the setscrews are M3x12mm & M3x14mm, and a standard M3 setscrew socket size is 1.5mm.
That assumes the 170 bridge screws are the same as the 270, which seems plausible. However, I've never had a decent hardware store complain if I bring in the part I'm trying to match so I can get a part to fit. You may feel "odd" hauling in your bass, but it's the best way.
The truss rod is supposed to be 5mm, though I think I saw a comment that the factory wrench is cut shorter than a usual allen wrench to fit in the pocket, so you might need to trim a "normal" one for the right fit.
The 270 manual (
unlike the 170 No, I'm just blind) also specs a 1.5mm and 5mm (#1.5 & #5 is what it actually says...) allen wrench as "accessories", so that would seem to confirm that.
RBX170 Manual
