What spark plug to use in 1998 suzuki rm250?

it's a BPR8ES plus

The recommended plug for the bike is an NGK R6918B7, it is expensive at around £35 from ngk but the bike will not function properly with any other plug. many people experience poor top end performance and end up spending money on unneccesary parts e.g. stator coils which can be avoided using the correct plug.