arnt spark plugs same you just screw the thing off the top if the suppressor cap needs it Hope that makes sense
That's what I thought but not sure if the modern smaller plugs are a smaller diameter at he top as well as at the bottom - was going to bid on some coil sticks for a conversion off a modern bike with 14mm plugs but unsure if the coil packs would fit 18mm plug tops. Auction just ended but I didn't risk it, they went cheap too!
I measured a selection of old plugs I had lying around. 10mm, 12mm and 14mm all have the same size of insulator. 24mm above the metal base and 10mm nominal diameter. I haven't seen an 18mm plug for years, they were used in tractors, dumper trucks, stationery engines and the like. They took the same size plug caps as 14mm plugs so I'd think the dimension of the insulator is the same on them too. I'm referring to the thread diameter but it occurs to me that you might be talking about the hex size. Either way the insulator's the same. Beware though that on some plugs the ferrule on the top doesn't unscrew, it's integral with the centre post with the electrode on the other end.
