I am missing a bolt for an old English gun. It had been badly buggered. But I have to plead stupidity because I put my damaged bolt in a safe place so I could recover it. Now I can't find it. I hate when that happens but I was knocked pretty dippy by the accident and the bolt probably needed to be replaced anyway as tig welding a new head and reshaping the bolt is an iffy enterprise. I'm going to try a machine threaded bolt, but I presume the thread is a British Standard Whitworth. All I know about Whitworth came while I was restoring a MGTD using Whitworth tools.I know nothing of the treads. 1)Will a modern machine thread bolt work in a Whitworth threaded hole? 2)Does any one know of a dealer who sells Whithworth screws or bolts?

The area the bolt screws into is on the tang and there is not much metal there to oversize drill and cut new machine threads. I am to not too crazy about drilling and re threading anyway as the fit is critical and if I don't line things up just right I'm going to have a problem with the gun.

Good luck, but I don't think you can presume anything about the thread on an old British gun necessarily conforming to any standard... What's the gun?

It's the Army&Navy I've been working on.

I would be most surprised if that is a Whitworth thread.
More likely to be a British cycle thread.
Depending on the date of manufacture, early like 1860 - 1900 could be anything because there was no standard threads & they made screws & taps from a screw plate.
O.M

Damn!! Things keep getting worse.

It's not getting worse, just more expensive.
O.M

I doubt that you will be able to find a US thread that will work in a Whitworth threaded hole. The US threads are cut with a 60 degree angle and a sharp vee top and bottom, while the
Whitworth is cut with a 55 degree angle, and the tops and bottoms of the threads are rounded. You probably can find taps and dies to cut Whitworths on the internet. A good investment for anyone who works on mechanical things is a book called "Machinery's Handbook". For your purposes, a used one several years old is good enough, as the basic info you need has not changed in the last 50 or more years.

Assuming you have a typical dial caliper, measure the ID of the screw hole. It will likely be near a fraction minus the thread depth times two. We can probably guesstimate a good fit of a standard bolt from this measurement. You may want/need to run a modern tap through the hole to make sure the new bolt fits reasonably. This is not the most technically "pure" repair, but a very practical one. Post the diameter and we will begin the rumination.

DDA

I'll do that! Thanks! I don't have a modern digital mic. I still use the old fashion calibrated mic which I have to put my glasses on to read. I keep thinking I ought to get a new modern mic, but I'm use to the old one.

I was thinking Whitworth used a 45 degree V, but there are many things I am wrong about.

I'm going to get that book.

When you get it back together don't forget to share what you learned on the DIY Gunsmithing forum. Photos are especially appreciated.

Steve

Pooch, do you know who made your A&N? Good chance it was Webley & Scott. And if it was, you may well be in luck. You might be able to find a gunsmith with a W&S bolt that will fit.

I'm with Rocketman. Find the closest available size, run a tap through and be done with it.

If it is an old Webley they used several thread forms if it is not a BA then the closest you may get is to look at it as a metric thread but with a Whitworth form of 55* not 60*.Basically the metric standard thread will probably do the job as it may well measure up as MM size .

I'm pretty sure it is a webley & Scott as the gun really has the appearance of a William Evans which is a W&S made gun.

For whatever it's worth the standard form of a US thread is not a sharp V. The normal form of a 60° US thread has the crest of the external thread flattened by 1/8H (H= height of the theoretical sharp V) & that of the internal thread flattened by ¼H. The normal "Tap" drill size or the normal pitch diameter for the external thread will ensure that neither ends up as sharp V.
Though somewhat dated now I have a set of thread spec book which I had to acquire when going through my machinist apprenticeship back in the 1960's.
If anyone has a specific thread they would like more info on let me know & I will look & see if it is covered. They do cover several British threads (including Whitworth) as well as metric & many unusual US threads even including light bulb threads.
Although not "Exact" a working solution for a tap drill for a 60° thread is to subtract one pitch length from the nominal diameter & then use the closet drill size possible. This will apply to either metric or US pitches, but remember that with US threads being given a TPI the pitch length is 1/TPI. Thus for instance a ¼-20 thread would have a pitch length of 1/20 or 050". A workable tap drill would thus be 200".

FWIW Whitworth bolt heads are the same size as metrics. It would not surprise me if the diameters were metric as well. I have nothing anymore to check for thread pitch but I'm guessing that would be TPI. And metric threads are the 55deg thing too. At least on bikes and motorcycles. Sorta like one from column A, one from ..................

have another day
Dr.WtS

I needed a tap when working on an Enfield sporter. These folks have a great assortment of tools and fasteners => www.britishfasteners.com

Thanks Wonk it's great to hear from you again. I know you are likely in pain because of Hillary's loss, but at least you haven't gotten on TV like these lame brain has beens and never wases to tell the Electors how to vote and blame Hillary's loss on the Russians and not the voters.

By the way I have converted from Browning to Italian style O/Us. I hate to admit it but you influenced me.

WTS: True metric threads are 60 degree just like US threads. There have been a number of different British thread standards used over the years, including Whitworth. There was a standard for cycle threads and one that is frequently used on models, British Association (BA) which is actually a metric thread.
Miller is correct that the US threads are technically flat on the top and bottom, but in my experience most are lathe cut with sharp Vees to eliminate the need to grind a special tool for each TPI to be cut..

Tom;
True, I have lathe cut threads with a sharp V tool. Note this will leave the sharp V Only in the root of the thread. When you get to the proper pitch diameter the crests will still have the flat. When you drill or bore the hole to the proper size for the internal thread those crests also will still have the flat. I have also lathe cut threads where it was a "Requirement" to put the proper flat on the tool for the part to met specs, just depends on it's designer & the use for which it is intended.
All the standard metric threads I am familiar with do have 60° V's. The Whitworths I am familiar with all had English pitches & 55° angles.
Mauser rifle barrels were fitted with a Whitworth thread having standard English pitch. Many have been rebarreled by US Gunsmiths with lathe cut threads having a standard 60° thread. They simply chased the thread until it would thread into the receiver & apparently no problems resulted from this practise.

Just an idea but is it possible to fill the hole with epoxy putty or the like, when cured, screw it back out and use a thread gauge on the imprint ?
I'm guessing a bit of oil or butter would stop the epoxy sticking fast and will help when it comes to winding the "blob" out.

El Garro's suggestion is not bad, but I would use cerrosafe instead.
Mike

http://britishfasteners.com/bolts.html

1.315.946.9400

7696 Route 31, Lyons NY 14489 USA

In most cases the British gun trade used three basic thread series; British Standard Whitworth [BSW], British standard fine[BSF] and British Association [BA].they tended to use off standard sizes for example BSF 9/32 or 3BA.By using off standard sizes,it was in my opinion an attempt to limit the ability of those outside the trade to repair or supply parts. This use of off-standard threads is very apparent in the thread series used on British cleaning rods and associated bore cleaning tools.
As stated by others due to thread geometry American and Unified threads will not interchange with same diameter/pitch Whitworth thread series.

When I was cutting metric threads for Italian bicycle and motorcycle pieces the microcomparator machine said that the original threads were 55deg on every part that I checked. Those were old manufactured parts. There were several metric "standards" in different countries and at some point in time the "new" international metric standards were implemented world-wide. If it's old Italian you'd best get it in a comparator.
The Whitworth (BSW) was 55deg, BSF were indeed 60deg and the BA were 47.5deg.
If you're gonna be cutting any of these you'd best get a copy of Machinery's Handbook and discover just what it is you have before you flip the switch. All of the formulas for dia/pitch/depth are in there.

JIC you don't know about this https://en.wikipedia.org/wiki/Optical_comparator

What Mr. Hebbes says about limiting availability is the essence of British industry. Especially since if it's Brit there is gonna be a LARGE replacement parts market.

have another day
Dr.WtS

I restored a MGTD including rebuilding the engine. I had a set of Whitworth sockets, so I thought I had it covered. Not so! Working on the car I would discover not only Whitworth was used but, English Standard and unexpectedly metric bolts and nuts were used. It drove me nuts. Years later I would discover that after WWII the English bought up German metric bolts and nuts cheaply and put them in their cars and machinery. I have been frightened of English mechanical things ever since. I'll get that book.