Hmm, not really imperial.
What is imperial?? Inch threads??
British imperial is typically what we have here and that is very different from USA inch sizes.
British is a 55 Deg thread and UN is 60 Deg thread.
Some of the pitches (threads per inch) are the same and they will screw together, but a lot wont.
The screws in USA pinballs would be No. 6 and No. 8 UNC, these are different from 5/32" and 3/16" threads in BSW and UNC.
The only exception I have seen is with Gottlieb pinballs made by Vifico in Spain, they have metric threads.