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alwaysride

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No, I'm not talking about clothing in the UK.

I'm asking about the threads on the bolts which are to hold down my factory hardtop.
Their diameter is a metric 8. But the metric 8 standard pitch and the metric 8 fine pitch don't have the right number of threads-per-inch.
Are these Whitworth? Where can I find a source for them?
 
What car is it for? It is only likely to be metric if it is a TR7/8. Anything earlier than that will probably use fine thread inch fasteners. 8mm is about 5/16, so it is probably a 5/16UNF (24tpi, as I recall). That would give you a spanner size of 1/2 inch to turn the bolts - does that sound right?

You can get them at a decent hardware store - Home Depot carries them I think too though I am suspicious of their fastener quality - should be good enough for something like a hardtop, but if you want to be sure I would suggest Fastenal or McMaster Carr. Fastenal seem to have a branch hidden away in most towns somewhere, which I find easier than mail order from McMaster Carr.

Hope that helps
Alistair
 
Actually True Value carries a pretty decent American Brand of hardware. /ubbthreads/images/graemlins/patriot.gif
 
Thanks for your help bash and glh.
Yes, 5/16 fine thread is the closest I've found, but it still is not the correct threading.

Last night I decided to see if I could make the threads work with 5/16. I tightened a 1/4 turn, backed off, applied oil, tightened again. It worked like a dream on the first nut. So on the second nut I went faster, tightening in 3/4 turns. Well, the threads got so tight that I couldn't back it off. The nut just spun in it's housing.
Fortunately I was able to pry away the housing.
So on the way home tonite I'll stop at True Value and get 2 5/16th bolts of the proper length, and one 5/16 nut.
 
You may want to buy (if you don't already have them) a 5/16-24 tap and a die. They will allow you to chase the existing threads so the new nuts/bolts will run freely.
 
Hi,

The previous request to know what kind of car we're talking is important! Without that info, we have a pretty hard time advising you very well.

Best I can do is tell you very few Whitworth were used on TRs. There was some limited usage on TR2 and early TR3 (mostly hydraulic fittings, I seem to recall), but other than that most TR hardware was NC or NF. There are some British Pipe Threads, but even those are very similar to NPC and often interchangeable.

Only on the later TR6 (1974-75?) did some metric fasteners begin to appear, and that was quite limited. Brake calipers are one place I'm aware of.

The hardtop for my TR4 (an early aluminum top) came with pretty beat up holddown nuts. They are "caged nuts" up inside the assembly and not easy to get to, to repair. I was able to *very carefully* tap them to 5/16 NC and am now using some stainless steel bolts with them. They were 5/16 NF originally, I can confirm because I have some of the original hold down bolts for reference.

I was careful about the caged nuts because once they spin you have little choice but to disassemble and repair/replace the cages. When cutting new threads or chasing old ones with a tap it's really easy to spin the nuts.

In the case of my TR4 top, because the mostly aluminum version, the steel support stays underneath are riveted in place. It can be more easily disassembled and reassembled, but what a pain just to replace a couple caged nuts. I'm not sure but the later all-steel TR4/4A/25/5 tops may be spot welded or otherwise assembled and harder to take apart and reassemble.

I'm not familiar with the hardtop assembly for TR6 (or TR7/8 for that matter).

/ubbthreads/images/graemlins/cheers.gif
 
Regarding spinning caged nuts... this is very true, you must be careful. I don't wish to discourage anyone from buying tap and die sets but this thread has now taken a turn where I would be remiss if I didn't make a warning.

The cheap tap and die sets you see advertised for prices below $40 are typically "tungsten steel" or similar. They are absolute garbage and can damage threads and parts. A decent tap and die set will be much more expensive. I prefer to buy taps made of high-speed steel. These will be bright in color and have a finely ground appearance. They are much sharper to start with and they stay sharp longer. Don't use the cheap (or dull) taps to chase threads in the captive nuts or you will surely damage them. Only use a sharp high-speed steel tap. If you can't afford to buy a high quality tap and die set, buy them as needed, one piece at a time.
 
/ubbthreads/images/graemlins/iagree.gif HSS is the way to go. I also agree that buying taps and dies on an as needed basis is the way to go. It's better to buy a few good quality taps, then winding up with a bunch of bad ones. On the Triumphs, there are only three sizes that are used extensively...1/4"-28, 5/16"-24, and 3/8"-20.

I also like to use Spiral Point Taps— Also known as gun taps, they have an angular point that shears and shoots chips out ahead of the tap. This keeps chips from clogging the flutes, thus reducing tap breakage. Even though they are use mostly in machine operations, for me, they make better hand taps then hand taps.
 
Sorry, I forgot to mention it is a TR6.
'spinning caged nuts', yes that was the problem with one of them and fortunately I was able to open the cage and let it out!

Yesterday the new window gaskets arrived and I put in the 2 quarter windows. Hopefully I'll have time to get the rear window in tonight.
 
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