Originally written: circa Aug. 1999
Last update: June 30, 2001 - fixed link back to index

Gentlemen, I am something of an expert on this boring subject so if you are interested please read on. If I can help anyone sourcing a few odd UK Nuts and bolts, email me the OD to within a few thou (MIL) and a reasonably accurate guess of the threads per inch and I will try to help.

In the later half of the second world war all British Military vehicles/Equipment were changed and were made using Unified UNF/UNC threads. This was because of commonality of spares to support the massive amount of equipment being given to the war effort by America. For UNF/C read ANF/C there were only very small technical differences in tolerancing. However, our national standards since the 1870's were British Standard Whitworth and British standard Fine. BSW / BSF These are similar to UNC/U NF but the main differences are the BS use a 55 degree flank and the UN a 60 degree, as do the current ISO Metric threads in Europe. However 1/2" BSW has different pitch to 1/2" UNC as do most of the BSF series. I would strongly recommend that you do not cross mix threads as they will be 20% weaker due to the different thread angles at the very best! Most coarse UNC / BSW threads are used into aluminium and this is where you will have problems with stripping and corrosion particularly with Stainless steel bolts.

All UN material Stock sizes used to carry a row of circles pressed into one face of the flats, but this has not been maintained due to imports. Another indication [but not foolproof ] is that if you measure a standard UN nut it will be exactly a decimal equivalent multiple of 1/16" size across flats. i.e. .4375": .500" : .5625" :625" : .750" etc.

Whitworth / BSF will not normally be so. e.g. .525", .600" .710", .820" etc. accross the flats. This is why the ZZZXXZZZ spanners / wrenches never fit ! MOST major UK car makers used UNF/C threads on NEW models after the war until the early 70's when they started to change to metric. This was due to a 1965 Government recommendation to convert to UN metric as 1st choice and UNC/F as second choice. However, the use of BSW/F carried on for Lawnmowers, Garden equipment and maybe some small car producers until the 80's when most went metric.

Although our favourite Marque, Jaguar were a low volume producer and often did not have the purchasing power I suspect to fully tool a part so would have to use other manufacturers components. As part of BL they were never really integrated. [I smile when I see all the worthwhile effort going in to reconstructing the build standard history, but stongly suspect that as Jaguar were building for a changing market requirement in the US, Australia and other places and coping with the supply problems we inflicted on ourselves at that time, the exact build standard was made up "on the line" from what was to hand to meet the various technical standards !]

Other threads
Pipe Connections
These used BSP threads. They were basically Whitworth 55 degree form but were nominated by the bore of the pipe. i.e. 1/4" BSP was about .528" O/D and 20 TPI This is why 3/16 Whit spanners often fit brake pipe unions etc try it!.

Electrical Fittings
Like the small size 4-40, 6-32 ANC/ ANF etc, we also had small screws for attachment. These were called British Association or BA and used a 47 1/2 Degree form. They use a number sequence and had their origins based on metric threads used in Europe for instrumentation. Basically most of Industry used the even numbers, 0, 2, 4 etc whilst the household electrical industries used the odds 1, 3, 5 etc. The thread number specified the size AND the pitch. There was no coarse or fine. You may find 2, 4, 6 BA threads in Lucas equipment built before the 80's. They are still freely available here.

There are other thread systems e.g. B S Cycle these have Whitworth 55 degree forms but nearly all have a constant 26 TPI except the very small. They some time crop up on old Motor Bike but not to my knowledge on cars.

Is stainless rustproof
Yes and no. It becomes rustproof by the formation of a very thin oxide on the surface {as does aluminium.} This is electrically non conductive and hence removes the basis for corrosion. If you scratch it and eliminate oxygen, e.g. keep it under water or oil , to prevent the formation of the oxide ,it will rust. As it does sometimes under washers. Certain chemicals EG chlorinated products will also cause corrosion on ss due to their reducing nature. If you use passivated Zinc plated fastenings these may prove better as on steel they are sacrificial as the plating dissolves to protect the bare steel.

I have listed below all of the relevant sizes for the various common threads. Hope this is interesting to at least one of you !