Elliott Omnimil 00 screw threads

This topic has 19 replies, 8 voices, and was last updated 25 March 2026 at 17:52 by aviv.

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23 March 2026 at 10:35 #841995
aviv
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@aviv
Sorry for the basic question, but does someone know if the bolts in the Omnimil are or Unified?

they are not metric for sure.

Thanks.
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23 March 2026 at 10:49 #842001
Wade Beatty
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@wadebeatty78296
I’ll go check
23 March 2026 at 11:10 #842004
Wade Beatty
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@wadebeatty78296
The belt tension holding bolt on the vertical head is 1/2 × 13 and one of the hex head bolts holding the flange for the horizontal drive is 1/4 x 20, both fit well on my 60 degree thread gauge set
23 March 2026 at 11:29 #842011
DC31k
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@dc31k
On 23 March 2026 at 10:35 aviv Said:

…the bolts in the Omnimil are or Unified?

There appears to be a word missing before ‘or’. Could it be Whitworth?

Find something with a hexagon head on it. If a fractional spanner fits, it is likely unified. If it has some strange A/F dimension, it is likely Whitworth.

Find something on it 1/2″ nominal diameter and measure the thread pitch.

Find something on it with a fine thread and measure the thread pitch.
23 March 2026 at 11:31 #842013
DC31k
Participant
@dc31k
On 23 March 2026 at 11:10 Wade Beatty Said:

…one of the hex head bolts holding the flange for the horizontal drive is 1/4 x 20, both fit well on my 60 degree thread gauge set

1/4 – 20 tpi is used both for Whitworth and unified. Your thread gauge test is incomplete as you did not assess the fit of the 55 degree Whitworth gauge.

If you are trying to do science, please do it properly.
23 March 2026 at 11:41 #842017
Wade Beatty
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@wadebeatty78296
Oh! Einstein shows up!
23 March 2026 at 11:56 #842019
Bazyle
Participant
@bazyle
An unified nut does not fit happily on a Whitworth bolt but works the other way round.

Worth knowing if you have a Boxford or SouthBend lathe as some bits don’t fit eg chucks.
23 March 2026 at 12:01 #842021
Howard Lewis
Participant
@howardlewis46836
In addition to the thread form, the pitch may give a clue, as BSF or UNF

Unfortunately, BSW and UNC tend to have same pitches for the same size, but 1/4 BSF is 26 tpi where 1/4 UNF is 28.

5/16 3/8

BSW BSF UNC UNF BSW BSF UNC UNF

18 22 18 24 16 20 16 24

Although a good guide, don’t be too fixated on the hexagon size. Sometimes you can come across A/F headed Whit form fasteners; fortunately only very occasionally! I met a 5/8 A/F bolt with a 3/8 BSF thread!

Howard
23 March 2026 at 12:31 #842027
Wade Beatty
Participant
@wadebeatty78296
A 1/4 x 20 NC nut fit on the smaller bolt and a 1/2 x 13 nut turned easy on the larger, also a 3/4 wrench fit fine on the hex on my mill.
24 March 2026 at 08:58 #842138
aviv
Participant
@aviv
On 23 March 2026 at 11:31 DC31k Said:

On 23 March 2026 at 11:10 Wade Beatty Said:

…one of the hex head bolts holding the flange for the horizontal drive is 1/4 x 20, both fit well on my 60 degree thread gauge set

1/4 – 20 tpi is used both for Whitworth and unified. Your thread gauge test is incomplete as you did not assess the fit of the 55 degree Whitworth gauge.

If you are

On 23 March 2026 at 11:29 DC31k Said:

On 23 March 2026 at 10:35 aviv Said:

…the bolts in the Omnimil are or Unified?

There appears to be a word missing before ‘or’. Could it be Whitworth?

Find something with a hexagon head on it. If a fractional spanner fits, it is likely unified. If it has some strange A/F dimension, it is likely Whitworth.

Find something on it 1/2″ nominal diameter and measure the thread pitch.

Find something on it with a fine thread and measure the thread pitch.

Indeed I meant to ask UNC or BSW. Fractional spanners fit well on the nuts and bolts. I will try to find 1/2 fastener on the mill and measure its TPI count with a thread gauge.

Aviv.
24 March 2026 at 09:29 #842141
Bazyle
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@bazyle
BTW are you a member of Groups.io/elliott
24 March 2026 at 10:05 #842145
not done it yet
Participant
@notdoneityet
On 23 March 2026 at 11:56 Bazyle Said:

An unified nut does not fit happily on a Whitworth bolt but works the other way round.

Worth knowing if you have a Boxford or SouthBend lathe as some bits don’t fit eg chucks.

Don’t need Einstein! 1/2” is probably the only size that has different pitch between Whitworth and UNC.

Whitworth is 12 tpi, while UNC is 13 tpi.

OOPS. Meant to quote Wade, not Bazyle.
24 March 2026 at 11:00 #842155
aviv
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@aviv
On 24 March 2026 at 09:29 Bazyle Said:

BTW are you a member of Groups.io/elliott

I’m afraid not. Could you share a link?
24 March 2026 at 16:52 #842186
Bazyle
Participant
@bazyle
https://groups.io/search

One of the files of the parts diagram quotes table locking screw of 1/4 x20 UNC.
25 March 2026 at 09:18 #842195
RobCox
Participant
@robcox
Having stripped down my Elliott Model 00 in the past to refurbish it I can say with all confidence that they’re UNC threads.
25 March 2026 at 09:29 #842196
aviv
Participant
@aviv
Thank you all!
25 March 2026 at 10:02 #842197
vintagengineer
Participant
@vintagengineer
Head size doesn’t always relate to thread size. Some early Morris cars had Whitworth headed bolts with metric threads.
25 March 2026 at 10:19 #842198
Bazyle
Participant
@bazyle
Aviv, assuming you are new to the Omnimill it may be worth checking these previous threads for interest.

https://www.model-engineer.co.uk/forums/topic/elliott-omnimill-00-axial-spindle-lock-ideas/.

https://www.model-engineer.co.uk/forums/topic/elliott-omnimill-modification/
25 March 2026 at 17:47 #842234
aviv
Participant
@aviv
Thank you.
25 March 2026 at 17:52 #842235
aviv
Participant
@aviv
And BTW, I’m also looking for an original slotting attachment for the Omnimil, so if anyone knows about one for sale I would appreciate a link.

Thanks.
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