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MG MGB Technical - Tap & Die Sets - Which one?


If I was to get a tap and die set; which one would be best for a 72 GT. In other words what is the best selection of sizes and combination of 'screw' types (unf, metric etc.)?

Is there anything else I should aim/look for when buying a set?


Iwan Jones

In the USA I would buy an SAE set or in your case UNF and UNC. Although UNC is uncommon in MGs it's nice to have. HSS should serve your purposes - no need to buy an exotic set as they last quite a long time. Always use cutting oil and clean them after each use and compressed air would be nice also. Keeping them clean makes them last a lot longer.
Mike MaGee

A UNF set is what you want for the 72 MGB the most common sizes used being No10 32tpi, 1/4" and 5/16" UNF. 3/8" is also used but not so common. HSS sets are available in these sizes and include intermediate and plug end taps (not spark plug) Have a look round, metric is nore common but you will come across UNF sets sometimes. If all else fails Namric will be able to supply. Make sure you get a good adjustable lever at the same time.

I don't think you will need die nuts but you can purchase individually if needs must
Iain MacKintosh

Don't waste your money buying HSS taps and dies unless you think you are going to be using them all the time, carbon steel ones are more than adequate for a casual user, you can buy a good carbon steel set of the useful sizes of UNF/UNC taps and dies complete with holders from Clark [Machine Mart] for less than 30. An equivalent HSS set will cost you in excess of 100.
R. Algie

Iwan. Ron is correct, the purchase of an entire set to get the few taps you will actually use is a waste of time. Iain has a good starting list for which taps to purchase and they will handle the majority of the jobs you will need to do. UNC taps are used when the bolt goes into aluminum which is mainly the starter bolt and the cross member to transmission bolts. Here in the US, any good hardware store will have the taps you need and you can buy them as needed. As to the carbon steel vs. high speed tool steel debate, Ron is again correct. However, here in the US the high speed tool steel taps are what is most commonly available and you have to spend time to find anything else. You have to go to a machinist's supply store or deal with one of the mail order companies, like Rutland Tools or J&L Industrial, to find carbon steel taps.

As to dies, you are better off replacing the bolts than attempting to rethread the worn or deformed threads. A cut thread is not as strong as a rolled or ground thread and, if you have to restore the threads on a bolt or stud, it will never be as strong as originally intended. Caroll Smith's "Nuts, Bolts, Fasteners and Plumbing Handbook" has some excellent information on this subject.

Les Bengtson

The other common machine screw size used on the MGB is a 2BA. This is very common on the carburetors and instruments. You will also see a few 4BA machine screws in the instruments, but I wouldn't suggest getting one of these until it is needed (perhaps never). Again, pick these up seperately rather than as a set. For the machine screws, a thread chaser or tap may be the better way to go than trying to find replacement bits. Regarding replacing or repairing/cleaning existing bolts, consider getting a suitable thread file. This can be used to clean straighten the threads if there is just slight damage to them. Anything that can't be brought back into shape with a few passes with the thread file, should be replaced. Good luck - Dave
David DuBois

It's the other way round in this country, unless you go to a specialist engineering supplier most taps and dies supplied to the DIY market are carbon steel, and if it doesn't have HSS engraved on it it's carbon steel.
David, sorry to disagree with you but to the best of my knowledge there are no BA threads on an MGB these small threads are deignated 10-32 UNF and are very close to 2BA but have 32tpi whereas 2BA has 31.35 tpi and a slightly different thread angle 60 instead of 47.5 degrees.
Ron [the screw thread anorak!]
R. Algie

UNF and UNC as others have said. Mostly UNF but certainly some UNC on starter bolt, gearlever etc.
How you buy depends a little on your view of tools; one off necessities or a collection perhaps for the longer term.
You'll need several sizes and just buying those loose from a specialist will cost as much if not more than a set from a more general supplier.
I bought this set recently for work on my B and it is of excellent quality with very nicely ground pieces,


Ron - I agree that 2BA and 10-32 are so close in size and thread count that they can be used interchangably, but I can't agree with no 2BA fasteners used in MGBs. The carburetors and fuel pump both use 2BA screws and the fuel pump also uses 4BA screws on one of the covers. There are also a few odd BSF, BSP and BSC threads to be found in even the latest 18V engines and on the shocks. Those threads shouldnt give anyone any trouble unless they do a lot of engine work, but the carburetors ond fuel pumps do need the occasional thread chased unless one is going to replace them with 10-32. Cheers - Dave
PS - I used to use 10-32 helicoils to repair bad threads in fuel pumps that I restored until I finally got a 2BA recoil kit from Uni-Thread.
David DuBois

Just to afirm David's input--the throttle adjustment screws on the HS4 carbs are certainly BA threads. Check archives under "Throttle screws", I believe.
Paul Hanley

Sorry, I should have said Carbon steel. For what tap & die sets sell for it's foolish not to buy a complete set with both coarse and fine.
Mike MaGee

I seem to recall quite a few UNC threads on the engine (head studs etc), so if you are planning to rebuild that then I'd suggest getting the relevant UNC taps as well as UNF.

I D Cameron

Apologies, forgot about the carbs being BA, but in 35 years or so of messing about with old cars I don't think I've ever had to use a BA tap or die, and I've a full set from 0-12 for model engineering, in fact going back to the original question I've hardly ever had to use a tap at all of any size in all that time, probably the cheapest option is to make a thread chaser from a high tensile bolt, cut a couple of hacksaw drifts longitudinally along the thread, and it'll clean up most threads unless they're badly damaged.
R. Algie

Ron - In many cases (especially in aluminum) the thread chaser is probably the prefered (not to mention safer) thing to use to clean out old threads. I have wound up having the threads in the aluminum fuel pump bodies foul in the taps and have had to repair an otherwise usable thread from running a tap through it to clean up the last 10% of the thread (I don't do that anymore). Thanks for the hint. Dave
David DuBois

This thread was discussed between 15/08/2005 and 17/08/2005

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