I machined an ordinary plug socket down to thin the wall down on mine to get at NGK plugs. It's not the best alternative if you can get one that fits correctly out of the box, but if not, then it is another option you could try. Any engineering firm could turn one down for you in minutes and it would save you a lot of work by hand to get it to fit.
Indeed, so if the Sealey plug spanner or whatever thin wall spanner you try still doesn't quite fit, we can always get it machined so it does
She worked!!! Next question: plugs I bought have the bulbous end which won't unscrew. The ones I'm removing have the screws showing. Are both ok without modding the coils?
Excellent news that the plug spanner fits - perhaps you could put a post about it on the 749/999 section? Are you sure the top doesn't come off the plug? I can't help thinking it's probably just very tight. If the coil is working properly with just the the threaded portion, I can't see how it can work with the top in place. The iridium plugs you've taken out are designed to last for tens of thousands of miles without attention, so although they look cosmetically rough, I'd be inclined to just stick them back in. If you do, do not alter the gap! They should give a fatter spark than the others, so improved starting, idling and throttle response .
Some plugs or version of the same plug type, Nippon Denso being an example, have moulded tops to the plugs and these will not unscrew as they are solid. If it is clear that you do not have a removable screw top to the plug then you will either have to "modify" it in some way, change the cap or machine off the top of the plug cap and either thread it as per an original or machine and knurl the top of the plug so that the cap will fit over the plug correctly and grip it in the correct manner. I have been caught out like this before so it is always best to check the top of the plug before purchase.
As standard on the 999, should it have the threads showing or the top left on? These ones are certainly not undoing.
This is the rubber part from inside the socket to hold the spark plug while lowering into the hole. This rubber part stayed on the spark plug when I removed the socket. This rubber part took about 30minutes to get out. This rubber part is a #&!*.