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5/16 x20 tpi thread size

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Brian lightfoot02/08/2014 20:01:49
21 forum posts

anyone recognise 5/16 x 20 tpi thread very close to m8 metric .A place to buy some bolts would be good.

all the best Brian.

Speedy Builder502/08/2014 20:22:44
2112 forum posts
146 photos

Just watch out, as your 5/16 x 20tpi may be 55degree thread angle and the 8mm will be 60degree.

Neil Wyatt02/08/2014 20:28:01
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18250 forum posts
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It will be either cycle thread (55 degrees) or UNS (unified special) at 60 degrees.

You may have to thread your own bolts.

Neil

JasonB02/08/2014 20:33:57
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18924 forum posts
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Are you spot on 5/16" ? if its a fraction more at 0.320" then 20-20 ASME is a contender. Whats the item that has the threade dholes in?

J

Brian lightfoot02/08/2014 21:19:19
21 forum posts

The items the holes are in is car mascots from the 1920s. one French and two English the bolts are way past the best so hard to measure the size. The nuts across the flats are larger than the 8mm that fits in the tapped hole in the underside of the mascots.

All the best brian

Michael Gilligan02/08/2014 21:31:00
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16420 forum posts
715 photos

Unlikely as it sounds, Brian; these are very probably Cycle Thread [as suggested by Neil]

I know you were after bolts; but you may be interested to know that RDG is listing 5/16" 20 tpi taps on ebay.

MichaelG.

.

Edit: Not now quite so sure about the Cycle Thread ... these are usually 26 tpi

... More digging required !!

Digging done [fairly quick, due to a lingering "folk-memory"] ... have a look at the middle of the first paragraph, here.

thumbs up

Edited By Michael Gilligan on 02/08/2014 21:39:03

Edited By Michael Gilligan on 02/08/2014 21:48:30

Brian lightfoot02/08/2014 22:03:06
21 forum posts

Good information so far. But I would like to find some nuts and bolts 3 of each would do.

Thank you for the replys.

Brian

Michael Gilligan02/08/2014 22:16:40
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16420 forum posts
715 photos

Brian,

This guy is probably the most likely source

StigFasteners

... But his ebay shop is currently closed.

MichaelG.

stan pearson 102/08/2014 22:33:46
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135 forum posts
2 photos

Brian

Have a word with Martin at Emkaysupplies.co.uk he will help you if he can.

Stan

ANDY CAWLEY03/08/2014 04:41:53
172 forum posts
47 photos

I suspect you are looking at a thread that complies with British Standard 86. My copy is the1956 version. It covers (among other things) a constant pitch series of threads of 20tpi of whitworth form, that is 55degrees.

I am aware of this because all GN and Frazer Nash motor cars manufactured up to the mid thirties had threaded components,as distinct from fasteners, at 20tpi.

http://www.tracytools.com/ stock taps and dies of this type.

Edited By ANDY CAWLEY on 03/08/2014 04:43:09

Edited By ANDY CAWLEY on 03/08/2014 04:46:28

Edited By ANDY CAWLEY on 03/08/2014 04:47:45

Brian Wood03/08/2014 10:28:02
2272 forum posts
37 photos

Brian and others,

Would it be heresy to suggest a Bodger's Lodge solution and tap the holes M8, using stainless steel bolts to hold the mascot?

Chasing old standards like that takes time and will of course be in the spirit of period matching as the National Trust approach, but I question whether that matters in this case.

I'll take cover now in the shelter!

Brian

Tony Pratt 103/08/2014 10:36:56
1237 forum posts
5 photos
Posted by Brian Wood on 03/08/2014 10:28:02:

Brian and others,

Would it be heresy to suggest a Bodger's Lodge solution and tap the holes M8, using stainless steel bolts to hold the mascot?

Chasing old standards like that takes time and will of course be in the spirit of period matching as the National Trust approach, but I question whether that matters in this case.

I'll take cover now in the shelter!

Brian

I was going to suggest exactly what you have stated, use something standard.

Tony

OuBallie03/08/2014 11:06:17
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1150 forum posts
661 photos

As an aside, I recently stripped the front bodywork off of my '35 Austin Seven, and the air was blue whilst doing so.

The previous owner, who did a body off restoration, used whatever bolts came to hand when putting things back, resulting in me being on an endless search for suitable Metric, Whitworth et al spanners.

Geoff - Relaxing before another session with the 'darling'

Ady103/08/2014 12:11:09
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3871 forum posts
522 photos

The previous owner, who did a body off restoration, used whatever bolts came to hand when putting things back, resulting in me being on an endless search for suitable Metric, Whitworth et al spanners.

I've mentioned these before

Stanley ratchet spanners

 

A mere 3 spanners will cover you from 5-24mm and fit every imperial or metric nut ever made

Great for dismantling old bits of kit with weird nuts and bolts

Edited By Ady1 on 03/08/2014 12:14:24

Brian Wood03/08/2014 12:13:46
2272 forum posts
37 photos

Hello Geoff,

When I was struggling for cash as a young fella in funding my first car, a 1937 Morris 8, I stripped down the bottom end of the engine with a hexagon stamped bicycle spanner and a hammer. Same tools to put it together again!

I did though have to fork out for a ring spanner or two to tackle the head bolts to decoke it.

Happy days

Brian

Russell Eberhardt03/08/2014 15:22:00
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2600 forum posts
85 photos
Posted by Brian lightfoot on 02/08/2014 21:19:19:

The items the holes are in is car mascots from the 1920s. one French and two English the bolts are way past the best so hard to measure the size. The nuts across the flats are larger than the 8mm that fits in the tapped hole in the underside of the mascots.

You don't mention the make of car but some cars of the 1920s and 1930s, notably Morris, used metric threads (strictly French Automobile Thread) but with Whitworth sized heads and nuts so that English garages could use their existing spanners.

It could be 8 x 1.25 mm. The thread form is close enough to be able to use ISO metric.

Russell.

Brian lightfoot03/08/2014 17:04:12
21 forum posts

One mascot is French peugot and two English ,<AEL> I could use metric bolts but I like things to be authentic as possible. One way of spoting fake mascots is by checking the threds .

Looks like I need to make some on the myford , Wish I had the Cri-dan I used when working for Rolls Royce Motors in Crewe.

Thanks for all the help Brian

John Stevenson03/08/2014 20:05:50
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Moderator
5068 forum posts
3 photos

M8 thread is 8mm x 1.25 pitch

or converted to English

0.3149 x 20.32 tpi

Compared to 0.3125 x 20 then you must have eyeballs like a vulture.

JA03/08/2014 23:36:55
983 forum posts
54 photos

Please note that British Cycle threads are 60 degrees and are generally 26 t.p.i. British Brass threads are Whitworth (55 degrees) and were generally 26 t.p.i. (The two are not interchangeable).

Having got that bee out of my bonnet, it was common practice, before WW2, amongst a lot of manufactures to use die boxes to cut non-standard Whitworth threads by just opening the box up or closing it down. These manufactures included AJS (the Wolverhampton company, not the later name owned by Matchless Motorcycles) and the Bristol aero-engine company.

Do you know the providence of what ever has this thread?

JA

Brian lightfoot04/08/2014 16:31:35
21 forum posts

John

The eyes are poor but I have a very good feel/tuch with threds as I used to cut them all the time when I worked on a machine.

All the best Brian.

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