Motorcycle threads...information from a pre 1930s booklet.....

British motorcycles used a variety of threads over the years, some a type that defies immediate identification......the 20 tooth thread used on Velocette driveside crankshaft nuts for example....
9/16" x 20TPI, 55 degree form....
Here I need to make a correction, brought to my attention by Dai Gibberson from his archival material on Velocette....
I initially commented that this was an Admiralty Fine thread and the chart is below, however it is also listed in the more comprehensive British Cycle thread chart provided by Dai and posted underneath this....
One can only guess whether the Cycle Engineers Institute who made out the chart from the sizes and thread types used on bicycles then later motorcycles in the late 1800s, early 1900s utilised this size from the Admiralty series.
I admit to having no idea when both threads commenced as such.
Thank you Dai....




















Illustrated below, is a Velocette KTT drive side mainshaft, re-drawn from an original blueprint that faded.

























So from a small book I acquired years back, the exact date of publication is not known and there are no clues in the book as to this year, I scanned some charts.
It is called "Screw Cutting" in Cassell's Workshop series.....
But there is a spark plug thread chart that refers only to 18mm spark plugs....no reference to 14mm types, so this gives a clue as well as a reference to Drummond 4" lathes which a check reveals were in the early 1920's and so I've loosely decided it must be pre 1930.....
Following are some charts scanned from the book, that will prove useful if you've not already got some...
Left click on the images to enlarge.....




































































The Brass threaded listed below is the thread that most of the diameters are 26tpi, and the CEI or Cycle threaded listed further below is only 26tpi in some diameters.










































These metric threads listed below are interesting, especially the 5mm diameter thread.
Currently in S.I units, the standard 5mm thread is 0.8mm pitch.
Looking at those in the chart, the International was 0.9mm pitch while the French was 0.75mm.
The Smiths chronometric speedo and tacho use a 5mm screw to hold the frame with the movement to the case. The pitch is 0.75mm, the instruments were originally French Jaeger......
Below is a scan from an original Smiths blueprint of the screw and of the diecast frame that the screw attaches to.....