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Bob uk
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Posted on Monday, 28 July, 2014 - 09:05:   Edit PostDelete PostView Post/Check IP

Screw threads

In the main from say 1945 the UK motor industry including RR move away from whitworth towards unified threads. Existing designs with whitworth threads were used along side New unified stuff. The later the car the more unified threads.
By 1960 brit cars were largely unified. From approximately 1970 they started to go metric.

Whit has a 55 degree included angle
unified 60
Metric 60

Lucas favoured British association threads 47 degree. In particularly 2BA and 0BA. O is about 1/4 and 2 BA is about 3/16 inch dia. Lesser amounts of.4 BA. Note even numbers. There are odd numbers which are hardly used.

At first look a nut is a nut closer inspection will revel marks such as nicks and rings these identify the thread family or type.
Bolt heads have numbers 8.8 means 8.8 tons. Sometimes makers names. Ruby Owen on the head is most likely unified.
No marks on bolts means bolt is not graded. Nuts are not load marked in general.

All sizes in brass plain steel plated steel stainless steel are available for the 4 thread familys.

Steel cheapest then plated then brass and stainless
stainless is double price of the cheapest.
In bulk say 50 a plated steel 1/4 nut is 5pence each and may 10p for 1 inch long bolt.
Handy sizes are 1/4 5/16 and 3/8 unified fine UNF.

Unified has a even finer thread which SU carbs use here and there.

Wikipedia do tables.

ANC/ANF threads are a cousin of unified the radius on the thread peaks and troughs is didifferent
But will fit. Take care if critical thread. American National fine and course.

British Standard Pipe is whitworth based. The size is the dia of the bore not the diameter of the thread. Some are tapered 7 degrees approx. These threads are often used for sump plugs especially tapered ones.

It is rare to find a thread that is not in regular tables.

(Message approved by david_gore)

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