RogerH Posted August 17, 2017 Report Share Posted August 17, 2017 Hi Folks, yesteraday I was reading a very(1953 ish) old NdV Laycock OD manual - it only refers to TS20 and Vanguards. In the section regarding the inhibit switches it made comment of the 16mm threads. There has been a lot of discussion about the switch thread as the it measures 5/8" x 13tpi. This thread form does not exist as a standard thread - OK they can be quite easily made (at a price). Now in the days of imperial measurements why do Laycock refer to 16mm. Just to confuse it further the thread pitch is not the standard 2mm BUT 1.95mm Not a lot of difference but a difference all be it. So no further down the road for this rather odd situation but at least the manufacturers were aware of this oddity. Roger It also comments about not bothering with OD on 2nd and 3rd as the OD ratio is the same as the gear difference. Quote Link to post Share on other sites
boxofbits Posted August 18, 2017 Report Share Posted August 18, 2017 Hi Roger I think I found the manual to which you referred. Maybe it was the manufacturer of the switches who decided to use a metric thread. Were the switches made by a foreign company? I also came across a motorcycle forum on threads and discovered metric threads were used as far back as 1939 in Britain. It is a mystery wrapped in an enigma especially when you find out that the bloke who invented the Laycock overdrive, Edgar de Normanville, was actually British! Kevin Quote Link to post Share on other sites
RogerH Posted October 22, 2021 Author Report Share Posted October 22, 2021 Hi Folks, I'm resurrecting this thread as it is doing a turn on another club forum and a thought came to me. The thread form is 5/8" diameter x 13tpi - this can be measured quite accurately. It obviously exists but is a special. The designer could have used half a dozen standard threads to work perfectly. Could he have use 13tpi because nobody else did and it may help to protect his patent. Curious Roger Quote Link to post Share on other sites
stuart Posted October 22, 2021 Report Share Posted October 22, 2021 2 hours ago, RogerH said: Hi Folks, I'm resurrecting this thread as it is doing a turn on another club forum and a thought came to me. The thread form is 5/8" diameter x 13tpi - this can be measured quite accurately. It obviously exists but is a special. The designer could have used half a dozen standard threads to work perfectly. Could he have use 13tpi because nobody else did and it may help to protect his patent. Curious Roger Possible or he just happened to have that size to hand Stuart. Quote Link to post Share on other sites
stillp Posted October 22, 2021 Report Share Posted October 22, 2021 (edited) 4 hours ago, RogerH said: Could he have use 13tpi because nobody else did and it may help to protect his patent. Or they were just trying to make sure that they were the sole supplier of replacement switches. On 8/18/2017 at 8:19 AM, boxofbits said: I also came across a motorcycle forum on threads and discovered metric threads were used as far back as 1939 in Britain. BA threads were originally proposed to the British Association in 1884, and formally adopted in 1903. They were based on metric measurements, converted to inches and rounded to the nearest thou! https://www.sizes.com/library/technology/thread_BA1.htm Pete Edited October 22, 2021 by stillp Quote Link to post Share on other sites
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