guys i have one question what difference is between 10.3mm 8mm and 9mm spark plug wires? which of them is better to replace stock wires on D15B

 

theyre physically larger...
larger wires can carry a greater current with less less resistance (basically)

Unless youre making gobs of power, new stock wires are just fine for your d15.
Using fatter wires will not give you more power, either.

 

stick with the 9mm, good for both stock and performance.
diffrence between them is give/carry out more spark thats all.