Can I use different spark plug

[ChrisCorbett]

I have decided to change spark plug whilst doing a mini service. The problem is I can only buy dpr9z from eBay as no high street bike retailer seem to stock them.
Can I use an alternative plug or will this affect the running?
I have no idea what all the letters mean but I can find similar named plugs but not with z at the end.
I wanted to buy a plug today and ride tomorrow

[ChrisCorbett]

Ok so a quick scan on the tinterweb tells me the z relates to the reach (21mm) so I'm guessing this is pretty crucial and can't see any other plug which has the same.
Guess I'll wait til new one arrives then.....

[hotbulb]

It seems to be a "half-threaded" plug, in NGK-speak. I'm not sure what that means- I think it's because there's an unthreaded bit near the tip, which would be fairly crucial. (I recollect coming across a discussion on this a couple of year ago, in relation tpo a Honda bike,but I can't remember what or where )