Hi All , Can anyone tell me the thread size and length of the screw in the front disc on the 1988 xj40 , my local dealer doesn’t stock it and said to try a parts place for one , and i have no idea what size to ask for . I was changing brake pads and noticed there was this screw missing. Part number SF605047J in the classic catalog . Thanks Mark
Hello mark …
I assume the “screw” you’re referring to is item no.10 on the diagram. Although it’s actually a flat head “bolt” (not having a tapered end that comes to a point) your correct that it is in fact called a screw in the parts diagram … hmm.
It’s purpose is to exactly locate the disc on the hub. I don’t know the size but it would be easy enough to buy a few short flat head bolts (metric/SAE ?) and find one that works. As far as the length, as long as it dosen’t bottom out before the head goes flush with the rotor you’re OK.
The tolerance between the diameter of the lug nut studs and the holes in the rotor is so close that in my opinion you really don’t even need it.
If you’re referring to #10, then Grooveman is correct. Its not actually necessary. That part is still available from Jaguar, though I doubt any dealer would stock it. I had one missing that I replaced a few months back on my car.
I agree with groove, the rotor sn’t going anywhere once the wheels on 
As usual, Bryan N has the skinny about this screw - his post from 2006:
Hello Mark,
I had the same “screw” issue on my xj40 1992, dimensions: 8*12mm. hope it will help.