Odd tap sizes

[DalboyParticipant @dalboy]

I was sorting out some of my taps and dies and came across two odd marked taps one being marked as 17/64″ 25 and a manufactured name Millennium.

The second is marked as 7/64″ and what look like JS&S Governor. It also has a small stamp that looks like the broad arrow but has circles at the tip and to trailing ends

It seems strange that no other marking

Any ideas on the sizes marked would help

[bernard towersParticipant @bernardtowers37738]

specials were made  by loads of companies to keep you captive for spares (coventry tool and die for one) so your hope of finding who they are for is pretty remote but the best of luck.

[GeorgineerParticipant @georgineer]

They may be examples of Whitworth threads which never made it into the British Standard. This page gives some details, though regrettably I don’t have a record of what book it came from:

That definitely isn’t the broad arrow, but presumably the manufacturer’s logo.

George

 

 

[DalboyParticipant @dalboy]

Thank you both. That answered why they are odd sizes

 

[SillyOldDufferModerator @sillyoldduffer]

Not too difficult to identify once right words are used in a web search.

JS&S was John Shaw and Sons, who, amongst many other things, made three models of brass petrol blowlamp:  Governor, Lamb and Anglo Swedish.   The broad-arrow with circles represents a James Watt style centrifugal governor, so I’m confident the tap is for one of the threads on a  Governor model JS&S blowlamp.

Likewise, Millennium blowlamps were made or rebadged by Lake & Elliot Ltd.   Reasonable to assume the Millennium marked tap is for a Lake and Elliot Millennium blowlamp.

In the past someone bought them to repair blowlamps.  Today, I guess a blowlamp restorer would be delighted to have them, otherwise they’re useless.  Though Brass lamps look gorgeous, I wouldn’t use a restored petrol blowlamp in anger – too dangerous.   Modern gas torches are much safer.

Whilst BS, NS, Unified and Metric threads are often found on parts other than fasteners, manufacturers often prefer proprietary threads, not necessarily for helpful reasons.   Using weird threads to force owners to buy OEM spares is bad.  Safety might be a good reason – a special thread might have anti-leak or other advantages, such as keeping Bill Bodger at bay!

Dave

 

[DalboyParticipant @dalboy]

Thank you Dave for the added information

[Nick Clarke 3Participant @nickclarke3]

Whilst BS, NS, Unified and Metric threads are often found on parts other than fasteners, manufacturers often prefer proprietary threads, not necessarily for helpful reasons.   Using weird threads to force owners to buy OEM spares is bad.  Safety might be a good reason – a special thread might have anti-leak or other advantages, such as keeping Bill Bodger at bay!

Whilst on the topic of William Bodger I have been told separately by two different retired GPO engineers that odd number ba threads (3/5/7) were preferred in exchanges to prevent bodging and theft of parts.

[GeorgineerParticipant @georgineer]

I’ve not heard that given as a reason.  Father (Portsmouth Dockyard apprentice, 1920s) told me that in general the odd numbered threads were used for electrical work, even numbered threads for mechanical or structural work.  It has certainly been borne out by my experience of old electrical fittings, both domestic and industrial.

I might add that I have a number of rather nice plated brass 8 BA screws from old telephone exchange equipment.  Probably other sizes too, but I would need to check the come-in-handy collection.

George

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