It has been proven in numerous threads on here, by people with measuring equipment, that the angle of the taper is EXACTLY the same.
However the contact surface of the angled part of the plug is slightly larger and smaller depending on the brand.

Hence there is NO PROBLEM whatsoever using these plugs in various brands of engines, no problem at all, as long as you do not overtighten the plug.

I wish people would stop perpetuating this myth that the one brand engine can only use this plug etc etc etc. A quick search on this forum will reveal pictures and measurements proving the angle of the taper is the same with OS vs Nova plugs.

The only reason I can see why someone would continue to put forward this myth is that they have lots of expensive plugs of a certain brand that they want to sell and make money off.