Servo holding nuts

Hello all,
I hope you are all safe and well.
As I am putting the car back together, I thought that I would put new fasteners all round.

I am stumped by the four studs that hold the servo to the pedal box. They are 3/8 but neither 24 nor 18 pitch!

Does anyone know what pitch? It seems to be 20 but would like confirmation before ordering online.


Well, 3/8-20 is a BSF or British Standard Fine thread. Older Jags '30s-'50s have plenty of them. I wouldn’t have thought an XJ would, but maybe the servo was sourced in the UK.
I have bought them from these USA sources.

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Might try a method I used for decades.

Take the “old” nuts to the best equipped hardware store in your town. Match the nuts to the suspected bolts.

You may or may nnt find a match and what the pitch is.

There is a pitch tool. Several pitches and sizes on one shank. and the key. may not cover a BS key…

last ditch run atap over the studs. Retread to order. Ns 20 or 24/ AKA course or fine…


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M8 would give you pretty close to 24 TPI and 3/8".


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which bolts are you referring to? - Is it really from the servo to the pedal box or rather from the pedal housing? They may have changed.

Good luck


75 XJ6L 4.2 auto (UK spec)

They are not on this s picture. See the 4 holes in the gasket between the pedal box and the servo, that’s what I am talking about :slight_smile:

I assume this is what you are asking about? This is a 1971 XJ6 servo showing the studs at 24 TPI. Some later brake components moved over to metric.


Yes, these studs. Well mine do not check out at 24, but at 20!! :frowning:

M8 has a thread pitch of 1.25. 25 mm (1") divided by 1.25 mm = 20 TPI.

3/8" = 9.5 mm.

Try an M8 nut on your stud - I bet it will fit.


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Now this makes sense, because this thing was on the car and I fitted new nuts ten years ago, and certainly did not go through all this research. I probably simply used metric…

Problem solved: M8 nuts fit perfectly. :slight_smile: