A 4.2 (mm) is a standard inch #8 size.  With a few exceptions, sheet
metal screws in Europe are what we term "soft converted" metric.  That
means an inch screw with a metric name.  If it a hex head, then it will
be a metic hex, but the shank is still basically an inch screw.

If you need a metric Phillips screw driver, I have a few for sale (NOS)
for $75.00 each ; )

For sheet metal screws
M3.5 = #6
M4.2 = #8
M4.8 = #10
M6.3 = 1/4

John

Looks like 4.2mmx16mm sheet metal screw, part# N 013 964 9, according
to my ETKA. Takes a whser under it, part# N 011 540 2.