There is 2mm clearance between the motorplate and idler gear, either a button head screw or a countersunk screw with a countersunk washer will be fine.
If you space the idler post the idler gear will not be meshing fully on the spur gear (ie only part of the spur will contact the idler gear) which could lead to extra wear and it stripping.
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Jonathan | Atomic-Carbon
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