Well I purchased them when I only knew the depth of my deck in inches and was really guessing, even thought they turned out perfect.
They are 1/2" 8-32 socket head cap screws -
and 1/4" deep inserts.
Measured, the screws are about M4s approx 12mm and the matching inserts are approx 9mm deep.
Just get inserts that are less than the depth of your deck. I would think M5s would be better, I had to use a small rubber/metal washer on the top to keep them from pulling through.
Also a TIP – Cut a screw as close to the exact length of the insert. After drilling holes to depth (just barely deeper than the inserts) put the screw in the insert and screw them into the board with that. DONT use the slot on the top, It’ll snap in half. Then just back out the screw and use it for the next one.
Just some info, in case it matters…
I just cruise, no hard carving. There is a spacer for the motor clearance. However i have 44 deg calibers. But i couldn’t get them to touch standing still and trying hard. Those wheel wells are the key I think.