Metric & Multistandard Component Corp. has been a good source for non US standard fasteners and tools for many years. Be aware, their prices listed online are list prices so actual costs may be less.
Here's a link to their metric and British thread pitch gauges:
http://www.metricmcc.com/
Many good quality 60° Unified Thread Pitch Gauges will have a 25 TPI blade. These may or may not work well on a 55° British thread because the bottom of these threads are rounded and some pitch gauges have sharp 60° V teeth.
The British systems of threads and fasteners was intentionally designed over the years to be different than any other national standard as a protectionist measure. Customers who bought mechanical goods made in the UK had to get replacement parts from the "Mother country".
For example, 17/64" is 0.2656" which is 0.0156 larger than 1/4" (0.250"). It's also 6.74624mm.
British hand tool nomenclature was unique too. Whitworth spanners (wrenches) are the diameter of the threaded fastener. For example a 1/2" Whitworth spanner fits a 1/2" bolt. Other systems use the distance measured across the flats on the hex head nut or bolt.
Chas. Colerich Oakland, CA USA
Dr. Paul B. Williams wrote:
> Morning folks,
>
> The discussion about the peculiarities of Whitworth 17/64" X 25 chainring bolts/screws for Chater Lea chainsets got me thinking about the need to find a good gauge or set of gauges to determine such things. Any suggestions?
>
> BTW I lost out on the bidding for the bolts on EBay - guess I am now going to have to turn to my mate Derek. Just out of interest does anyone know of a supplier of Whitworth dies - a quick Google search showed that a 17/64 X 25 die can be obtained (borrowed?) from the London Douglas Motorcycle Club! Maybe worth a membership???
>
> Boy do I miss having Sheldon around!
>
> Paul Williams,
> Ottawa, ON, Canada