Inlet Manifold and Water Pump Plugs Thread Pitch?

Can someone confirm the thread pitch on those various brass plugs as found around the inlet manifold and the small outlet of the water pump? The ones that are around 5/8" (0.625")? I can’t tell if they’re 18 or 20tpi (or something else?) using my Starrett gauge. One of the major suppliers identifies them as 5/8-18 UNF but I’m suspicious of that. I happen to have a die in that size but when I try to fit one of those plugs in to it, it won’t fit – unless forced. I ask here because one of the threaded plug holes on my inlet manifold (XK120) has slightly messed up threads from my having removed the plugs as part of an engine tear down. I believe I can still save the threads but only if I can be assured of using the right tap.


They are 3/8 BSPP 19 TPI on, as near as dammit, 41/64"dia.
A 3/8 BSPP tap and die in the toolkit allways handy when fetteling -The Jaguar…
NOTE BSPP or a later designation BSPF NOT BSPT.
Be aware that the electric temperature sender fitted to later manifolds, MK11 etc IS 5/8 UNF
Peter B
Word to the good, a split die enables a water take off, etc, to be formed slightly larger than standard
dia, this helps if the thread in the manifold is not 100 per cent.

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Here is a US source for the 3/8 BSPP tap.
page 7-720 in their catalogue.,-15,800
major diameter is .6560" BTW.
If you need a 3/8 BSPP hex head pipe plug and copper seal ring, they are on page 1-156.
I have bought so much from them that they are beginning to suspect they are carrying Jaguar parts. Don’t tell them and give the game away. :grin:

Beautiful!! I knew you guys would come through! This site is the best. In some ways I have a far easier time getting the RIGHT answer here in 2019 as opposed to 1979 when I first started wrenching on these. Thank you.

On a side note, it would be nice if one or more of the major suppliers could put together a tap and die set specific to these cars. A sort of all-in-one set for at least 90%+ of the fasteners one could expect to encounter when doing a restoration. I would have bought one. Either that and/or a new whole-car fastener set. Early on in my car purchase it was tempting to just change over the 1/4-26 tpi fasteners that secure my front wheel well splash guards to 1/4-28 fasteners as one example. And who would really know? But in hindsight, I’m happier I didn’t and for those less patient, I’m sure others have. Having a full tap and die or fastener set would make things much easier for all and dissuade others from veering off with non-original fasteners. I’m also thinking of this because having done restorations on pre-war Indian motorcycles – where fasteners large and small are all 24tpi – it was nice to know I could order a whole-'bike set of new fasteners made to pre-war specs. Just a thought as I haven’t seen anything on the market like this.

I’ll wager all the info is contained in the archives: one could assemble said set, and market it.

However, I’m thinking it’d be a hefty price tag.

Moss Motors does that for MGT series.
I made a list of what I would need and placed an order with

I can’t say every single one is available, but a vast array of these taps can be found on the McMaster-Carr website. Certainly anything BSPP or BSPT, which are common in industrial hydraulics, is available there. The shipping world has gotten so competitive that I am generally receiving things from them on a next-day basis 6 days a week.

McMaster - Carr. Well I learned something new there. Thanks Mike. I order from them all the time but never would have thought they’d carry a tap in BSPP standard. Good to know. My go-to people in the past have been British Tools per Rob Reilly but McMaster is so much faster. I’ve also had good luck in the past with Victor Machinery Exchange out of Queens, NY.