Imperial countersunk screws (socket head) have an 82º head. A #6 should has a .307Ø theoretical sharp head. If you were to measure one, it could be as small as about .263 but your c-sink has to be .307Ø or the top of the screw will lie above the top of the work surface.
Thank you Robin, and Errol, for taking the time to find the info and reply.
I am still slightly confused (I might not have asked the right questions). My situation is that I'm using a Hammond aluminum enclosure - dimensions shown here:
(150KB) The #6 machine screws supplied (Phillips) to attach the 1.5mm thick face panels actually sit proud of the panel.
I'm having some custom panels made up and wanted to get the screws to sit flush with the panel. I've had a test panel made with 82deg countersink angle (sorry, I found that I already had that info) and a maximum diameter of 0.240". Now I have the panel back, the maximum diameter seems too big with the screws in place - there is an easily gap around the edge of the screwhead. I must have given you the wrong information, as the 0.307Ø is more than the 0.240Ø that I've tried.
As Robin said, .307 is the max head diameter for a #6 flat head hex socket screw. For a standard #6 flat head Phillips or slotted machine screw the max head dia is .279 . If the head height is greater than the thickness of the panel you'll have to either put a small contersink in the threaded hole, or get hold of the flat head screws often seen on electronic equipment panels where the head is truncated at the intersection of the head and body. Clear as mud?
Normal flat head: ________ \ / \ __ / | | | |
Truncated flat head: ________ \______/ | | | |
Does anyone one know what this head style is called?
I now realize I've been asking the wrong question - sorry to you all. Looking at the Hammond enclosure diagram more carefully it says #6 screw, but #4 head. Indeed, the head is the same diameter as some other #4 screws I have around (but the thread is wider than those). I think this is what you mena by the truncated flat head.
Sorry for the confusion! So my question should have been this:
What is the max diameter of the head of a #4 flat head Phillips machine screw?