Sure enuff ,
It was unclear exactly which of the several different type screws on the R-390 faceplate the OP had in mind .
I was just generally setting some of the improperly used terms straight .
Flat head and oval head screws fit into a countersunk seating and the appropriate washers are pre- formed to fit that seat . In the US that is usually an 82 degree included angle , some aircraft apps use 100 degree due to material thicknesses.
Again , the pitch is the reciprocal of the Threads Per Inch spec . A 20 thread per inch thread has a .050" pitch , a 4-40 screw would have a .025" pitch etc.
An 8-32 screw is not a 32 pitch .
The proper star type lockwashers for flat head screws are usually thinner than standard star lockwashers .
http://www.marshallshardware.com/products/productList.aspx?uid=2-301-452-312Binding head screws are a different item altogether but most military rack applications use binding head screws rather than countersunk , flathead screws and countersunk trim washers . When countersunk screws are used for faceplates , an OVAL head screw is often preferred . The oval head screw is similar to the countersunk flathead screw but it has a rounded off top surface rather than the flat .
Many, very many rack applications do indeed use 8-32 screws .
Length call out for both types of screws is the
grip length . Countersunk screws are actually very close to overall length called out as the threaded portion is actually shortened by the head thickness . Binding head screws length is the actual the length below the head .
Also worthy to note that Stainless screws are generally not as strong in tensile as their carbon steel counterparts . Probably of little concern for radio faceplates but in other applications the stainless may not hold up as well as the carbon steel fasteners .
Vy best 73 to you , Gary