Fin screw: Countersunk M6x20 (top of head to end of thread), DIN 965 (ISO 7046), Phillips 3 drive.
Strap screw: Cheese head M6x20 (thread shaft length, bottom of head to end of thread), DIN 7985 (ISO 7045), Phillips 3 drive.
Both screws are stainless, they should be AISI 316 (A4) but the usual grade is AISI 304 (A2), that may work depending on the manufacturer.
Plenty of information I’d say!
NOTE ON SCREWS:
It appears that not many people know which screwdriver to use, and do an improper job screwing and unscrewing.
There are two main kinds of drives that resemble a cross, Phillips (the ones the surf industry uses) and Pozidriv, you can distinguish these by 4 small grooves between the larger grooves forming a cross. The screwdrivers are not interchangeable!
You can’t properly assemble a board without the right screwdriver, and using the wrong tools you’ll run the risk of loosing fins and opening straps, while you mess up the screws drive with sharp burrs that can mess up other equipment.
More on this here.