Ps....this part is different to the rubber boots on the track rod ends
Edited for clarity. I thought Siri did quite well tbh.

Have vx suddenly gone retarded over night or sumat. Slough have a new parts donkey with an appalling attitude. Couldn't or wouldn't give the best price on oil, as the 20litre drum I asked about was cheaper than the first "best deal" he quoted me.
Anyway, never mind that.
The rubber boot for the centre tie rod to steering idler ball joint is the pesky item in question. Its much shallower that a tre rubber boot. So they're no good, as they swell up like a balloon when the parts are done up then split.
Measuring is tricky as the old one was toast and its got a tre one on there now and is buggered, hence the need for the correct part.
Or.... A part number.

It would be so nice to quote the part number to knob features in Slough. Bit like the door check strap bush. Oh no sir, you need to but the complete mechanism to get that part.

and the aux belt tensioner pulley.