fasteners used in old Pioneer valve amplifier

Hi all,

I'n new to the group, recently joined to seek some information on my current project.

I'm in the process of rebuilding an old Pioneer SA-400 amplifier and am having trouble identifying the fasteners used through-out the unit. They're not standard metric threads, though the verniers measure the diameter of the 2 sizes used as 3mm/4mm. most of them are self cutting screws, but even the ones that aren't have the same thread.

They don't seem to be BSW or UN threads either. I've been down to the local screw shop and they are also unable to identify them.

is anyone able to help identify the screws?

thanks.
 
I usually use self tapping 2 or 3 mm screws on steel or metal and they work fine.
You must be careful when it comes to fasten on plastic parts or You end up breaking something.
Perhaps I would use Inox types on the outside in order not to rust.