BSW/SAE Threads – UK Restorations

Interesting that about the Merlins, as the BA and BSW/BSF thread systems differ in more than just diameter and pitch, having different thread angles (60 degrees and 55 degrees, from memory) and different spanner sizes.
If you work on the basis that if something can be installed wrongly, then it will be, and also that there is no underestimating human stupidity, then Merlin mechanics must have had an, er, interesting time. 1/4 BSF and 0BA aren’t that far apart.
Just to confuse matters, 0BA has a 1mm pitch and a 0BA nut fits a 6mm metric coarse thread – rather loosely and with much recuced strength. Therein lies a particularly nasty pitfall. Don’t ask me how I know this…

William

Yes, I have to agree with you on that. There is even one oddball on Rolls-Royce engines which is that the 2BA fittings have a 3/16″ BSF size hexagon which is slightly larger than the standard BA hex, great idea, because one set of spanners does the whole job? Not so, because a Merlin also has 0,1 and 3BA nuts which all have the standard BA hex. Work that one out!
Peter

When I started as an apprentice I bought a set of these. I think they were £42 for the set (which was over a weeks wages in those days!). Nice to see that they are still available (and stll as expensive!).

All the BA bolts are still available. For aircraft quality got to Light Aero – www.lasaero.co.uk

For commercial, many places will do them, but prices vary. I am considering stocking them for panel projects and cockpit restorations.

Bruce

On a related note, what is the availability in the UK of the smaller length BA bolts. I have seen some for sale on the net but they seem very expensive.

Chris,
And any other ‘tool freaks’ out there! :p

There is an absolutely fabulous tool shop near me that sells just about everything and at reasonable prices too.
Let me know what you are looking for and I can go and see if they have it/ can get it.
Failing that I am sure my Dad and my father in law have old spanners in the garage / shed that you can have, I was going to borrow them my self in case I ever got chance to use them but I guess you would use them before me! 😮

Cheers, Alan

I ask because I’m rebuilding a control column and handles out of a FN120/121 turret that I actually got through ebay from fellow forumite Merlinpete. I am planning to install them in a FN121 that is entirely SAE. They’re almost an exact match to another set found in Canada, but all the fasteners are BA. After searching for over ten years I jumped at the chance when I found this pair.

I did a bit of googling and read that all major sub-assemblies of the Canadian Lanc’s were interchangeable with the British so that they would not have to send for spares.

It sure must have been an interesting time at the repair depot!

Regards,

Interesting!

I was just wondering about the interchangeably of parts between Canadian and British built aircraft during WWII.

….and you got a sack of information on Thread forms, interchangability, joint strength and where to get BSF Spanners!!! 😀
I would guess that aircraft design would have been standardised but that is just a guess.

Chris

Mmmmmm, maybe I haven’t been looking for BSF spanners with as much dedication as I work with them?
Thanks all for the pointers, I thought they were a rarity but have been able to get hold of BA quite easily.
Problem is, my spanners are very much a mixure of odds and ends, many have been ‘modified’ to gain access to those hard to reach (and see!!) areas and have probably been used on an almost daily basis since they were new. Indeed the jaws have suffered and the chrome is long gone!

Thanks to those friendly chaps at the CAA, we will be stripping our Avons down on a yearly basis now and I thought a nice new set of quality spanners were the order of the day 🙂
Of course the museum pieces will be retained for those special, dark, hard to reach corners 😀

Chris

Britool still do BSF/BSW spanners, as do Elora and Gedore.

A really good tool shop will often still stock them.

Bruce

Interesting!

I was just wondering about the interchangeably of parts between Canadian and British built aircraft during WWII.

Fair point. The spanners I bought in April were in fact for an ex-RAF Vulcan chum (no…hang on, he wasn’t in Star Trek. Oh look, you all know what I mean) who’s got his own small engineering business.
My own spanners in this size came frem my late father, and some of them go back to the days when he served his time as a motor mechanic with Blakes (Liverpool car dealer) back in the 1920s!
As long as the jaws haven’t opened out they should be OK (and I’ve got a few like that)….but a nice clean well-finished spanner can be a joy to work with. I know where Chris is coming from.
Sad, aren’t we?

William

If they are opening up i would replace them i agree. Ive got some ancient tools laying around here that i still use. Although not for anythinng to do with aviation.

Why upgrade if they still work is my question?

Fair point. The spanners I bought in April were in fact for an ex-RAF Vulcan chum (no…hang on, he wasn’t in Star Trek. Oh look, you all know what I mean) who’s got his own small engineering business.
My own spanners in this size came frem my late father, and some of them go back to the days when he served his time as a motor mechanic with Blakes (Liverpool car dealer) back in the 1920s!
As long as the jaws haven’t opened out they should be OK (and I’ve got a few like that)….but a nice clean well-finished spanner can be a joy to work with. I know where Chris is coming from.
Sad, aren’t we?

William

It would be nice to own a set where the chrome isn’t all peeling off you know? I think my spanners are as old as the Avons I’m spannering 😀

Cheers
Chris

Why upgrade if they still work is my question?

Worth setting up an automatic search on Ebay too. I’ve often found interesting or normally hard to find stuff on there.

Roy.

Thanks for the idea.
I’m more likely to frequent Airshows but I have friends that can look out at Bike / Car shows for me.
It would be nice to own a set where the chrome isn’t all peeling off you know? I think my spanners are as old as the Avons I’m spannering 😀

Cheers
Chris

Bought a very nice set of unbranded BSW/BSF combination spanners, I presume Indian-made, from the Classic Bike Show in Stafford in April for £14.99. Haven’t got the trader’s name now, but in general a classic car or bike show seems the best bet for a reasonably-priced set.

William

Another point of interest is that it’s dead easy to get brand new BA sockets and spanners but almost impossible to get BSF / Whitworth?
Unless anyone knows where I can get new BSF and Whit tools from? I’d be eternally grateful

Chris

I can see the point in using BA for the smaller thread sizes, and the risk of trying to force a nut onto the wrong thread would be minimal as a result.
I used to have a stash of aerospace grade BA fasteners in the garage that would have lasted me the rest of my life, and probably that of the children. They dated back to the time when everything was going metric in the early 70s, and apart from the desire to standardise on metric specifications generally there was the particular risk of the 0BA/M6 mismatch – hence great handfuls of them could be carted away from Filton with impunity. 2BA, incidentally, is quite close to 3/16 UNF, but you’d have to be a cack-handed mechanic beyond all reason to force one on t’other.
Alas, we had a break-in a few years back and the chest full of BA and cycle thread fasteners went.

William

Interesting that about the Merlins, as the BA and BSW/BSF thread systems differ in more than just diameter and pitch, having different thread angles (60 degrees and 55 degrees, from memory) and different spanner sizes.
If you work on the basis that if something can be installed wrongly, then it will be, and also that there is no underestimating human stupidity, then Merlin mechanics must have had an, er, interesting time. 1/4 BSF and 0BA aren’t that far apart.
Just to confuse matters, 0BA has a 1mm pitch and a 0BA nut fits a 6mm metric coarse thread – rather loosely and with much recuced strength. Therein lies a particularly nasty pitfall. Don’t ask me how I know this…

William

Not sure if this rule of thumb carries through to other types but on the Rolls Royce Avon particularly you go down to 3/16 in BSF sizes and then step down to 2BA and then 4BA etc for the smaller stuff. I’ve never encountered 0 BA yet to be honest? As long as you follow that rule then the pitfalls can be avoided.

Interesting that about the Merlins, as the BA and BSW/BSF thread systems differ in more than just diameter and pitch, having different thread angles (60 degrees and 55 degrees, from memory) and different spanner sizes.
If you work on the basis that if something can be installed wrongly, then it will be, and also that there is no underestimating human stupidity, then Merlin mechanics must have had an, er, interesting time. 1/4 BSF and 0BA aren’t that far apart.
Just to confuse matters, 0BA has a 1mm pitch and a 0BA nut fits a 6mm metric coarse thread – rather loosely and with much recuced strength. Therein lies a particularly nasty pitfall. Don’t ask me how I know this…

William