Question

what affect the fuel air mixture ratio existig in thespark plug gap

Answer 1

It can depend on the engine: new spark plugs might be pre-gapped for a V-8 engine, installing all 8 plugs unchanged; however if installed in a 6-cylinder engine, all (6) plugs would require re-gapping.

A spark plug gap gauge is a disc with a sloping edge, or with round wires of precise diameters, and is used to measure the gap.