1/2 BSP on Austin 7?

[Howard Wright]

Hi Hedd and Dickie

I thought BSP and Whitworth had the same thread form?  A quick Google search seems to confirm this but I’m no engineer. So what is the difference please?

Cheers

Howard

[dickie65]

We might have to Start a new Thread for this !!
I will have to consult my specialist books.

[Charles P]

Hi Hedd and Dickie

I thought BSP and Whitworth had the same thread form?  A quick Google search seems to confirm this but I’m no engineer. So what is the difference please?

Cheers

Howard

Same 55 degree form as BSF and BSW.
Very different in the meaning of the nominal size

c

[Howard Wright]

Hi Charles

Thanks.  I now realise that I had thought that a 1/2” BSP was 3/4” diameter but it is substantially bigger.

Hence Hedd’s comment!

So Jon I have no idea why you have a 1/2” BSP tap  .

Cheers

Howard

[dickie65]

BSTP
The british standard whitworth form of thread with 55 deg thread angle is used. one sixth of the sharp vee is truncated at the top and bottm, the threads being rounded equally at the crests and roots to a radius equal to 0.17329 times the pitch.
The standard taper of the BS taper pipe thread is 1 in 16.
The flanks of the BS whitworth thread make equal angles with the axis of the pipe or screw. ( bs no 21-1938 )

BSW.
this thread form has been standardised by the british standards institution ( bs no 84-1940 ) and it is used for bs whitworth, bs fine and bs pipe parallel. it is of symetrical vee form with an angle between the flanks measured in the axial plane of 55 degrees.

There are three different fits for BSP though.


information taken from engineering workshop data, Arthur W Judge
Caxton Publishing April 1950.

[Bob Culver]

The topic of pipe threads is very confusing and although the situation can be fathomed by pondering the data it is seldom explained directly. 1/2 inch is based on the outside diameter of a nominal 1/2 inch bore thick walled wrought iron pipe as in use from sometime well back in the 19th Century. So the size is much larger than the name. The taper threads theoretically provided a watertight joint when forced together, although hemp or somesuch is usually necessary. Some medium point of the taper is adopted for the parallel version, used where adjustment is necessary and for railings etc. a parallel thread of sorts can be produced by mal adjusting  two piece taper die sets.
just to be awkward the American system is not based on the 55 deg Whitworth thread and differs in dimensios, some pitches etc. Machinerys Handbook defines a myriad variants of the basic spec.
To add to the confusion, here the traditional and still standard BSP threads have been allotted nominal metric sizes! So oldies like me get funny looks when we ask for some 1/2 inch BSP fitting.
Incidentally I recall some Seven blocks have plugs for the gallery below the ports. Are these 1/2 BSP or smaller?

[Howard Wright]

Hi Bob

The oil galley plugs on the crankcase are 1/8 BSP and 1/4” BSP

Cheers

Howard

[Ray White]

This may be of assistance.

https://www.rowse.co.uk/blog/post/how-to...p-fittings

[Hedd_Jones]

Bob, 

Hemp and Stag B is the stuff for sealing iron pipework. Just made and fitted the pipework to the roller.

Ray,

Those of us who use it regularly, can identify it using mk1 eyeball. Though I did have to resort to the caliper to something I thought was 5/8 BSP I found on my Merryweather steam pump. It wasn't, it was 1inch 14tpi. Using a split die, a jubilee clip, and a stilson I managed to make it 5/8 BSP so the tail and nut I had bought for it in error fitted. Saved a shed load of work in the lathe. The annoying thing was the other male threads were all 1/2 BSP.

[Ray White]

I get confused between BSP, BSB, and BSC. I understand the differences but not always the application. I found some rather nice slightly domed bolts on the front wing stays of my Swallow. I misplaced a nut and it nearly drove me to distraction finding a replacement until I realised they were 26 tpi . cycle thread.!