U can used NGK Iridium in Yours Yamaha YB-100 Bike too. But for it U can used extra Washer on it then insert it Plug into holder.
For the Best used of NGK Iridium plug in the 2-Stock Bike is that U also use pour Oil mixing with super petrol, actually Plug give extreme Electric current to burn out fuel inside Head Cylinder. That Oil mixing keep Lubricating your piston very well.
In that case then U hv needed to Shorten Ur Muffler (Bansari) for Quick Exhaust of smoke.