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screw type abbreviation

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gerry madden24/02/2020 14:19:08
95 forum posts
43 photos

I have an assembly drawing that calls up a couple of countersink head screws, eg. 1/4BSFx1/2 which is then followed by the suffix 'ASH'. Can anyone tell me what the suffix means ?


JasonB24/02/2020 14:22:01
17321 forum posts
1865 photos
1 articles

"Allen Socket Head" would be a possibility.

Howard Lewis25/02/2020 17:58:13
2927 forum posts
2 photos

BSF = British Standard Fine

BSW = British Standard Whitworth.

BSP = British Standard Pipe

BA = British Association

UNF = Unified National Fine

UNC = Unified National Coarse

UNEF = Unified National Extra Fine.

NTP = National Taper Pipe

Whitworth form (and BSF and BSP   threads are 55 degree while Unified form are 60 degree angle. BA form are 47.5 degree angle. Metric are 60 degree form.

BSW and UNC thread pitches are often the same, as are many BSF and UNF, but DO check! BSP and NTP are different thread form, and the TPI varies as well.

Metric threads are defined by diameter and pitch, so that you can have the standard Metric Coarse, say 12 x 1.75 and a fine version as 12 x1.5 or even finer at 12 x 1.25.

There is no reason why diameter and pitch cannot be non standard. Some Myford lathes used 7/8 x 12 tpi, while then later ones used 1 1/8 x 12 tpi. This is quite common practice for screw fitting chucks for lathes.

Allen Socket Head screws are often referred to as Capscrews. Csk signifies Countersunk head.And then there are Button head and Dome head varieties as well!



Steviegtr25/02/2020 18:07:09
827 forum posts
187 photos

Also BSB

British Standard Brass. Not sure if it's the same as BSP.

Isn't there more as well. CEI cycle thread ???


Edited By Steviegtr on 25/02/2020 18:08:22

Howard Lewis25/02/2020 18:19:49
2927 forum posts
2 photos

British Standard Brass is a Whit form thread but with a constant 26 tpi.

Cycle Thread is also 26 tpi, but is 60 degree thread form, so not really interchangeable.

The other variations on the Whitworth thread form are the Model Engineer threads. Most are a constant 40 tpi, while others are 32 tpi.


JasonB25/02/2020 18:28:20
17321 forum posts
1865 photos
1 articles

Gerry was asking about the suffix (bit at the end) "ASH" not the actual thread form abbreviation (BSF etc).

Edited By JasonB on 25/02/2020 18:28:39

old mart25/02/2020 19:58:13
1252 forum posts
116 photos

Cycle threads, that is BSCy come in a large variety of pitches, not just 26tpi. Motalia have a number of thread charts within their site:

Edited By old mart on 25/02/2020 20:03:28

Tony Pratt 125/02/2020 20:13:39
1029 forum posts
3 photos

'ASH' sounds like a non standard call out just to confuse every one, who's drawing is it?


Derek Lane25/02/2020 21:20:58
307 forum posts
70 photos

I also would go with Jason,s explanation. I know I am mainly woodworking but I have spent 25+ years in plant repairs dealing with many types of fittings.

Georgineer25/02/2020 21:35:32
332 forum posts
16 photos

Posted by Howard Lewis on 25/02/2020 17:58:13


UNF = Unified National Fine

UNC = Unified National Coarse

UNEF = Unified National Extra Fine.

A lot of people think so, but this is from an American source:

" Some confusion over the UN designation exists. Some people think it means Unified National based on the fact that three national entities came together to unify their thread standards; thus: Unified National Screw Thread Form. By reading the [standard] B1.1 this is not supported; rather UN is the abbreviation for UNIFIED."

I think the 'National' is a hang-over from the American National series of threads, which was replaced by the Unified Thread Series in 1949.

BSC (sometimes called BSCy) replaced CEI threads (Cycle Engineers' Institute) in 1950.

British Standard Brass thread is not a British Standard...


not done it yet25/02/2020 21:41:41
4168 forum posts
15 photos

I expect it will be like these.


Likely fewer available, rather than buying that many, from other suppliers

Steviegtr25/02/2020 22:56:17
827 forum posts
187 photos

Dad worked at the British screw company, later to be GKN. Guest , Keene & Nettlefold if I have spelt it right. Anyway he always said it was United Nations fine course etc.


gerry madden25/02/2020 23:05:37
95 forum posts
43 photos

JB and NDIY, looks like you were bang-on. When I looked carefully at the dwg it was a socket head type. Thank you for the confirmation.


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