I measured mine, and found these measurements, using McMaster's drawings as my guide:
length 10mm (not counting the collar; 15mm with the collar)
collar height 5mm
head height 8mm
head diameter 21mm
There is about 25mm of depth available for the threaded part, so you can go longer than 11mm, which I would recommend. You also have plenty of room for a larger head diameter.
There is also a thin plastic washer pressed or threaded on the screw on the other side of the cover that serves a keeper, so you don't lose the screw. It would be a good idea to make something like that so you don't lose the new one.
The M6 x 15mm screws that Eeyore located on Amazon.co.uk are also available on the US Amazon, and would be just right: [You must be registered and logged in to see this link.]