MGB: What system is used on MGB bolt size?

Happy 4th everyone. As this is my first British car (71 MGB) I am not sure which system of bolt size was used. I have done some minor service work on the car and used USE wrenches but wasn't sure. I checked the archives but figured someone wouldn't mind answering this.

About all but one obsure and seldom messed with item are American sizes.

Std inch.

a few odd pieces might stil be Whitworth (not worth buying Withworth wrenches though) and I've found some...not original,,,that are metric (late jet adjusting hexes on HS4s seem to like a 17mm --I use a crows foot--and the fixture panel bolt for the clutch flex line (in the chassis) seems to be 20mm.)

No, they're Canadian sizes.

Righe Derek, it just trickled down to us.

I find that the previous owners of my car liked to add a little sport to the whole bolt thing. Every standard imaginable can be found.

robieusa Wrote:

robieusa Wrote:

Not sure how that smiley face with the shades got in my post, was supposed to be a ). John, Mac thanks thats what I kinda thought. Derek what would those sizes be?, 10ay, 12ay, ect, ect. Just Kidding!

Most everything on a B or a Spridget is in standard American/British sizes, but there are a few things that you will find to be related to the fuel system that are in a system called Whitworth. Not many but a few. I bought a full set of Whitworth tools about forty years ago and they aren't worn out. In fact some have never touched a fastener.

There are some variations on the thread shapes for the American stuff. Something called Unified is actually interchangeable with American fine threads as opposed to American standard course stuff. The Unified threaded nuts usually have a set of interlinked circles on one hex flat.

There are no Metric fasteners on the cars as far as I know, but some replacement parts made in God knows where might be of metric dimensions.

Jack

CaptainAL Wrote:

B) B) Thanks Rick. Jack I'm glad you joined in. Been watching your posts and see you know your way around these machines. I once was a Volvo/Toyota/Ford guy.Alex gotta love those Beverly Hillbillys. One of my all time favorites. Fancy Eatin table! Pot Passers, handy pockets for the scraps.

for a list of British threads in the MGBs, mostly in the engine, see the article, British Fasteners Used on the MGB in the Other Tech Articles section of my web site: http://homepages.donobi.net/sufuelpumps/ What is not listed in this article are the fittings on the SU fuel pumps, which are all British Standard Pipe (BSP). The Unified threads came out during WWII in an effort to standardize all threads used by the allies. It is based on the American threads, both National Coarse and National Fine. The Unified threads were designated UNC and UNF. As Jack stated, the Unified fasteners had special markings on them. This can be seen on the rear axles and all lug nuts on the late TD and the TF and an explanation can be found in the shop manuals for the TD and TF.
Cheers,

next week we'll discuss the cursed pozidrive.

twigworker Wrote: [quote]
Most everything on a B or a Spridget is in standard American/British sizes, but there are

go and get figging technical on us, eh? Unified thread. Geess!

You can disassemble most of your car with a few sae sized wrenches, sockets and extensions and a few cans of PB Blaster. The posidrive screws will annoy you - look like phillips - they're not. Can't tell you what it takes to reassemble yet ;-)

I'm serious Mr. Mac!

If you don't believe me, listen to Dave.

The Unified system uses a slightly different profile for the tops of the thread peaks and in the valleys. It is a tad bit more rounded, I think because they figured that doing it that way would prevent some of us Yankees from stripping things out all the time. :-)

I suspect that using the British Pipe system on the fuel pumps and the Whitworth sizes on a few other things had something to do with keeping the Union Boys quiet.

Cross my heart!

Jack

If I remember correctly from my 4 years living in England, there is actually a Unified Fine thread and a Unified Course thread. Look at the bolts holding the windscreen frame to the body at the sides, I'm pretty sure I remember these being course thread, I'll need to go look at a frame in the garage to be sure. Nearly everything on the B is UNF, close to SAE Fine thread, but not exact.

CaptainAL Wrote:

Slightly off thread but what is this "crows foot" tool some of you refer to? Never heard of it until I came on this forum. Anyone care to enlighten this puzzled Brit?

Steve

Hughie Wrote:

ddubois Wrote:

I'm not sure what they call them in the UK. Steve, let us know.

gooser Wrote:

Derek up North Wrote:

B) Thanks for all the info. Been a good post EH