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

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

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.

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

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

Brian,

This guy is probably the most likely source

StigFasteners

… But his ebay shop is currently closed.

MichaelG.

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

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

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.

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.

If you wish to be authentic surely the mascot should be fitted with a stud and not a bolt. I have owned a number of vintage cars with mascots on the radiator cap and not one of them used a bolt.

The Peugot one would almost certainly used French Automobile Thread and the AEL one was probably BSF. If you can tell the difference between 8 x 1.25 French Automobile Thread and 8 x 1.25 ISO Metric without a shadowgraph or equivalent you are a better man than I.

Russell