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8BA to 1/8 Whitworth


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Nearly Done19/06/2019 16:03:31
14 forum posts
3 photos


new to this site and just wondered what the consensus is on Doing a mod to a small brass or Nickle knurled nut 5mm dia 6mm tall, which is tapped for 8BA but needed to be 1/8" whit.

Drill size for 8BA is 1.8mm

Drill size for 1/8" Whit is 2.55mm

Im thinking it could be ok to drill out and re-tap.

any comments appreciated.

JasonB19/06/2019 16:06:51
16269 forum posts
1721 photos
1 articles

Should not be a problem

Nearly Done19/06/2019 17:07:12
14 forum posts
3 photos

Thanks Jason for quick reply

I'm waiting on a thread gauge but just measured the male thread OD at 2.2mm got a feeling it could be 3/32" whitworth. Not 1/8"

Nigel Graham 219/06/2019 17:54:38
386 forum posts

In which case, oh dear!

It's the root diameter of the existing thread in the nut that would count first.

8BA - 2.2mm nut root

3/32" - 2.4mm screw OD (neglecting crest rounding, probably insignificant.)

So if the intended fitting is indeed 3/32" BSW with only 0.1mm (0.004" a side you'd be heavily "modifying" rather than replacing the existing thread, which suggests having to replace one of the two fittings to be sure of a secure fixing.

JasonB19/06/2019 18:20:46
16269 forum posts
1721 photos
1 articles

Yes if it is 3/32 and the nut is showing signs of wear you won't have much to retap. If it is something you are restoring and want to keep the old nut then drill it out say 3.5mm and solder in a bit of brass that ha spreviously been tapped, depending on use you could even Loctite the sleeve in.

Nearly Done19/06/2019 18:27:17
14 forum posts
3 photos

Thanks for replies

It's the male stud that is original, I had a nut made thinking it was 8 BA but sadly does not engage,

If I ran a 3/32" whit tap into the new nut will it just mess it up ?

or is it start again?

roy entwistle19/06/2019 21:21:05
1033 forum posts

How about trying it ? cheeky

old mart19/06/2019 22:06:35
576 forum posts
54 photos

The 8BA is 0.086" od and the tapping size for 3/32"W is 0.070", it will end in tears. 1/8"W would be ok, as the tapping size is more than the od of 8BA @ 0.0984". 

Is there room to drill and tap to a larger size, and Loctite in a plug to d&t to 3/32W?

Edited By old mart on 19/06/2019 22:09:02

Howard Lewis19/06/2019 22:12:05
2337 forum posts
2 photos

Either bush the new nut, or make a new one.


JasonB20/06/2019 06:59:04
16269 forum posts
1721 photos
1 articles

I'd just open it out to tapping size for 3/32 whit and tap, if it has enough bite for the job in hand all well and good, the fact it is a 6mm long nut will help . Ff you mess it up you can still sleeve it or make another

Nearly Done26/06/2019 15:53:09
14 forum posts
3 photos

Well the plot thickens I bought 3/32" whit tap set drilled a small piece of brass rod and managed to tap enough to cut off and try (6mm long)

I goes on but very sloppy fit I'm wondering if the male is an odd ball size.

glad I did not run the 3/32" tap through the nut I bought.

SillyOldDuffer26/06/2019 16:31:55
4713 forum posts
1010 photos

Could be a case of faulty thread identification - it's not easy, what with Whitworth, UN, BA, NC and others in coarse and fine variants. Can you put up a photo of the male thread next to a mm rule so we can eyeball it? (Howto post photos here.)


Nearly Done26/06/2019 17:01:59
14 forum posts
3 photos

Let's see if this works hopefully a picture will emerge!img_0852.jpg

Nearly Done26/06/2019 19:37:56
14 forum posts
3 photos

Should have said OD of thread is .085"

looks to have 44tpi

Nigel Graham 226/06/2019 21:10:10
386 forum posts

This is a rum 'un....

44tpi is not a standard Whit-form thread. Studying the Mechanical World Year Book 1957, and your supplied information, I reckon the following:

It's actually metric but not from the modern ISO Series.

So:... 7BA? BA is in fact metric, based I think on the old, Swiss Thury thread.

OD for 7BA = 2.5mm. Pitch = 0.48mm.

Enlarging the page to read the photo better...

Pitch by the rule: a gnat's crochet under 0.5mm.*

Dia. measured = 0.085 " = 2.16mm but could be accounted for by over-rounding when cut, and by wear in service. The thread does look as if it's seen a year or two.

So I reckon the nearest standard to the photographed screw is 7BA.!


(Long-time listeners to I'm Sorry I Haven't A Clue will know that unit of estimation...)

SillyOldDuffer26/06/2019 21:47:22
4713 forum posts
1010 photos

Looks a bit metric to me too! What's the item? I'm wondering if it's antique, continental or perhaps a trade specific thread.

This table identifies some arcane possibilities. Whitworth Instrument & Thury are both candidates.


Nearly Done26/06/2019 21:47:49
14 forum posts
3 photos

Thanks Nigel,

Its a rum'um. That thread was cut c1910.

strangely the nearest thread on gauges I have is metric .6 60deg but that's a 3.5mm ISO !

Nearly Done26/06/2019 21:50:59
14 forum posts
3 photos

Thanks Dave I'll take a look, it's off an old English Fishing reel.

Michael Gilligan26/06/2019 23:01:36
14014 forum posts
608 photos
Posted by Nigel Graham 2 on 26/06/2019 21:10:10:

Enlarging the page to read the photo better...

Pitch by the rule: a gnat's crochet under 0.5mm.*


In an attempt to calibrate the aforementioned gnat's appendage:



I reckon five pitches to be 2.947mm [ish]

2.947 ÷ 5 = 0.5894

So [allowing for perspective effects, and general incompetence on my part] I think the pitch might be either 0.6mm or 43tpi

BUT if it started life at 5BA, it must be very worn.



Edited By Michael Gilligan on 26/06/2019 23:03:03

JohnF26/06/2019 23:09:09
864 forum posts
102 photos

Looks like a Hardy Perfect strapped tension adjustment lock nut, most threads on these are BA except the centre locking screw in the spool and these are either 1/8th or 5/32 LH Whitworth. The thread does not look worn to me so I would make a new nut from nickel silver or brass -- the were made from either material but usually match the adjuster which on your reel is Nickel Silver.

Worth noting on many of these and gun locks the threads are very near but often oversize due to wear on the dies use -- interchangeability was not a issue back then.


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