Whitworth, BSF and BA

by Annette Flottwell

So you have bought imperial sockets and spanners but there are even weirder bolts?

Series Threes and later Land Rovers seem to Contain only UNF/UNC threads or metrics, the imperial bolts should fit to AF ( across flats) sized spanners. Unfortinately, this is not all. Ever came across these 'specials' in the parts catalogue?

In a Series One and many later Land Rovers you'll encounter sooner or later bolts that don't seem to fit into any system. This is the day when you'll have to identify Whitworth, BSA and BA threads and boltheads.

BSW (British Standard Whitworth) are the coarse threaded bolts that attach for instance, the fenders of a Series One to the bulkhead. Or hold the seatbox. One side of the gearbox studs is Whitworth, too.

BSF (British Standard Fine) is the finer version of last-century British threads, invented because Whitworth can be just too coarse. BSF bolts hold many engine and gearbox parts in a Series One.

BA is the real weird stuff. The higher the number, the smaller the pitch. It is called 'metric', because division of an inch are base on the logarithm of 10. No I didn't drink anything special, but don't ask me how this was invented. BA lives in electric equipment and in Series One carb linkages and surprisingly many other small bolts. BA cannot be measured with a thread gage and cannot be replaced with anything.

There is no real difficulty if you have Whitworth, BSF and BA spanners like the one in the picture. But these are almost impossible to find these days, unless you visit flea markets or invest enormous sums in mail orders.

How to read this table: All sizes we came across so far in Julie's Series I are bold. This table is only meant for bolt heads and spanners, not for the threads. For BA I recommend a 3BA/2 BA double open ended, they're cheap and available in the UK. Note: Do NOT use 12 star sockets (these should be avoided anyhow) to replace any of the red sizes. These red sizes are only meant for spanners and hexagonal sockets

Whitworth

BSF

BA

in mm

decimal inches

BSW/BA Spanner

will fit Spanner

7.1628
8.2296
8.636
9.271
10.4648
11.303
13.335
15.24
18.034
20.828
23.368
25.654
30.48

But the main tool to dismantle the odd rusty exhaust manifold is the angle grinder. If you don't want to cut metric threads in the original parts or you simply have to find the right fastener, this is the moment to get your thread gage. Buy one, this 2nd hand gage was £6. You'll need it if you want to buy bolts cheap from the tractor dealer instead of a Series Land Rover pharmacy.

The outer diameter of a bolt gets you exactly nowhere, for instance 2BA, and 3/16" Whitworth and BSF have almost the same outer diameter. If your gage fits nowhere, it is really metric or BA. Metric you can rule out measuring the outer diameter. 2BA has 31.4 threads per inch (no joke) 3/16" Whitworth has 24 tpi (threads per inch) and 3/16" BSF has 32 tpi.

Outer diameter

BSW tpi

BSF tpi

BA # tpi

BA mm

Inner diam. BSW

Inner diam. BSF

Inner diam. BA

4.1
4.7

5.3
6

Please note: I've only listed diameters you might come across in Land Rovers. This does not list all you find find in a model train or army tank.

Here is a very useful link to all thread data, including tap diameters. Most of the above was compiled from a broken 'Shetack' disk calculator donated by Tony Astridge. Use the linked table and common sense for further reference.

Van der Valle (in Dutch, but all the numbers are international :-) )

So before you think of re-tapping a thread, make sure you got the right tap. Is the pitch and the diameter correct? If a new thread has to be cut in a replaced captive nut, use for a larger Whitworth threads at least a taper and a botoming tap. A broken tap can be replaced, but not your bulkhead.

If you really have to cut a larger thread into a buggered one, use a tap with the same threads per inch. That is, cut a larger BSF in the former BSW so that you have to remove only very little of the original steel. If that doesn't work, drill outat least the old OUTER diameter to use as the new INNER one!

If this doesn't help, keep in mind that in early Land Rovers ANY aircraft / Fire Brigade or Navy thread was possible - even metric thread was found. They had to use anything that was available after the war. No choice.

Dies can be very usefull to lenghten a thread on a linkage or bolt. For repairing an existing thread the bolt should be held in a lathe or vise and the die must be held perpendicular, check twice. If you remove lots of steel insted of rust, check again whether you've got the right die!

NEVER try to cut a thread with a different pitch but the same diameter. You'll £$%& both bolt and thread and you'll make sure to face an even bigger problem when you have to dismantle that bolt again, if you haven't lost it.

What to invest: 2nd hand good quality taps are between 50p and £2 in the UK, for dies count on £2-£3 if they are still OK. Bring some useful souvenirs from your next visit to Billing!

Have fun and work safely!

by Annette Flottwell

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