MilesA Posted January 10, 2021 Report Share Posted January 10, 2021 One of the joys(?) of owning a 60 year old car, is finding the unique changes made by POs. Wanting to change the gear knob it soon became clear the thread was not the standard 7/16 x32TPI ME or even the later more common 5/16 x 18TPI UNC. Lots of measuring and head scratching later I concluded it was probably 7/16 x 20 TPI British Cycle Thread. Having spent a few quid buying some nuts with this thread from a specialist supplier, I verified this afternoon this is in fact the thread on the gearstick. Given the difficulty in tracking down these nuts seems like a pretty obscure choice for a replacement thread (or do I just have an obscure gearstick / gearbox?). Now to track down a tap... Miles Quote Link to post Share on other sites
RobH Posted January 10, 2021 Report Share Posted January 10, 2021 7/16 x 20 is UNF Miles...... Quote Link to post Share on other sites
RogerH Posted January 10, 2021 Report Share Posted January 10, 2021 Hi Miles, you appear to have it all ocnfused. As stated by Rob 7/16 x 20tpi is UNF 7/16 British Cycle thread is 26 TPI is the norm but 20tpi can be obtained but for very odd uses. When dabbling with TRiumph stuff always opt for the cheapest variety UNF not Cycle. Roger Quote Link to post Share on other sites
Ralph Whitaker Posted January 11, 2021 Report Share Posted January 11, 2021 14 hours ago, MilesA said: One of the joys(?) of owning a 60 year old car, is finding the unique changes made by POs. Wanting to change the gear knob it soon became clear the thread was not the standard 7/16 x32TPI ME or even the later more common 5/16 x 18TPI UNC. Lots of measuring and head scratching later I concluded it was probably 7/16 x 20 TPI British Cycle Thread. Having spent a few quid buying some nuts with this thread from a specialist supplier, I verified this afternoon this is in fact the thread on the gearstick. Given the difficulty in tracking down these nuts seems like a pretty obscure choice for a replacement thread (or do I just have an obscure gearstick / gearbox?). Now to track down a tap... Miles Tracy Tools, Torquay. Everything on their website and fast delivery. Ralph Quote Link to post Share on other sites
MilesA Posted January 11, 2021 Author Report Share Posted January 11, 2021 (edited) Well, I have two 7/16 x 20tpi taps and neither fits the nuts I bought which do fit the gearstick. Also, none of the common 7/16 nuts I have fit the gearstick otherwise I would not have had to look for anything different! Surely if 7/16 x 20tpi was the same as UNF then the nuts I have would not need to be manufactured. Difficult to argue with the physical evidence. It has been suggested that the angle of the thread on BSC is different to equivalent UNF. Miles Edited January 11, 2021 by MilesA Quote Link to post Share on other sites
MilesA Posted January 11, 2021 Author Report Share Posted January 11, 2021 2 minutes ago, Ralph Whitaker said: Tracy Tools, Torquay. Everything on their website and fast delivery. Ralph Thank Ralph. Tracked them down last night and ordered a 7/16 x 20tpi BSC tap. We will see... Miles Quote Link to post Share on other sites
Ralph Whitaker Posted January 11, 2021 Report Share Posted January 11, 2021 3 minutes ago, MilesA said: Well, I have two 7/16 x 20tpi taps and neither fits the bolts I bought which do fit the gearstick. Difficult to argue with the physical evidence. It has been suggested that the angle of the thread on BSC is different to equivalent UNF. Miles I am not saying that yours is the same, but I had to extend the thread on my gearstick to accept the saloon gearknob with the overdrive switch built in, and mine was 1/2 inch x 20 tpi, not 7/16th. Ralph Quote Link to post Share on other sites
Lebro Posted January 11, 2021 Report Share Posted January 11, 2021 (edited) I thought the TR3 gear lever thread was fairly coarse, possibly UNC ? I say this because at one point I was thinking of fitting a Saloon gear knob with the overdrive switch. That had a finer thread, so I ran a suitable die down the gear lever to "override" the existing thread. In the event, I did not use the saloon one, but now have a wooden one with a metal insert which I made, & threaded to match the new thread on the lever. I can measure what I have today & report back. Bob. Edited January 11, 2021 by Lebro Quote Link to post Share on other sites
Ralph Whitaker Posted January 11, 2021 Report Share Posted January 11, 2021 10 minutes ago, Ralph Whitaker said: I am not saying that yours is the same, but I had to extend the thread on my gearstick to accept the saloon gearknob with the overdrive switch built in, and mine was 1/2 inch x 20 tpi, not 7/16th. Ralph Apologies, I have just been and checked and you are right about it being 7/16ths Miles, but I am da---d if I can find the die I used. Ralph Quote Link to post Share on other sites
RogerH Posted January 11, 2021 Report Share Posted January 11, 2021 (edited) Hi Miles , you have found an oddity. The 7/16 CE thread is very much the same as the 7/16 UNF except the core diameter. The CE is 0.008" bigger than the UNF. Also if the gearstick is chrome plated that will also add to the core diameter. So you may have a UNF thread with too much chrome. Or you have infact a CE thread - but that wouldn;t make sense. If you have 7/16unf die - run it down the thread so that a UNF nut will then fit. Roger Edited January 11, 2021 by RogerH Quote Link to post Share on other sites
Lebro Posted January 11, 2021 Report Share Posted January 11, 2021 (edited) Just checked mine. 7/16" dia, X 20 TPI which is 7/16" UNF. So I believe the original TR thread was coarser than this probably UNC at 14 TPI. Perhaps someone before you has done what I have to mine ? Edited January 11, 2021 by Lebro Quote Link to post Share on other sites
Ralph Whitaker Posted January 11, 2021 Report Share Posted January 11, 2021 15 minutes ago, Lebro said: I thought the TR3 gear lever thread was fairly coarse, possibly UNC ? I say this because at one point I was thinking of fitting a Saloon gear knob with the overdrive switch. That had a finer thread, so I ran a suitable die down the gear lever to "override" the existing thread. In the event, I did not use the saloon one, but now have a wooden one with a metal insert which I made, & threaded to match the new thread on the lever. I can measure what I have today & report back. Bob. Found the invoice for the tap and die I bought, and you are right Bob, my thread was 7/16 x 32 tpi and I bought ME (model engineer). Ralph Quote Link to post Share on other sites
Ralph Whitaker Posted January 11, 2021 Report Share Posted January 11, 2021 (edited) 25 minutes ago, Ralph Whitaker said: Found the invoice for the tap and die I bought, and you are right Bob, my thread was 7/16 x 32 tpi and I bought ME (model engineer). Ralph Just to convince myself here it is screwed on to the gearstick. Only just seen that it is stamped WF, don`t know what that is but it was supplied as Model Engineer. So there are at least 3 different threads then depending on the age of the part, 7/16x32 ME, 5/16x18 UNC, & 7/16x20 UNF. Ralph Edited January 11, 2021 by Ralph Whitaker Additional thoughts Quote Link to post Share on other sites
Lebro Posted January 11, 2021 Report Share Posted January 11, 2021 My saloon (2000 Mk2 1972) gear knob is definitely 20 tpi & the TR thread was something different, I thought coarser, but may have been finer. Quote Link to post Share on other sites
david ferry Posted January 11, 2021 Report Share Posted January 11, 2021 (edited) My understanding is that the only correct thread on the top of the sidescreen gearstick is 7/16 x 32tpi. Certainly, that's been the case with all of the gearboxes I've seen over the years. Of course, anything could have happened over the years...... David Edited January 11, 2021 by david ferry Additional thoughts Quote Link to post Share on other sites
RogerH Posted January 11, 2021 Report Share Posted January 11, 2021 And to muddy it further - my TR4A Gearstick is 18TPI so coiuld be BSF or 5/16 UNC or even 5/16 Whit More investigation to do. Roge Quote Link to post Share on other sites
RogerH Posted January 11, 2021 Report Share Posted January 11, 2021 (edited) Hi Folks, it doesn.t help Miles but mine is 5/16 UNC 18 tpi I wonder what medication the chief gearstick thread cutter was on at the time. Roger Edited January 11, 2021 by RogerH Quote Link to post Share on other sites
Hamish Posted January 11, 2021 Report Share Posted January 11, 2021 5 minutes ago, RogerH said: I wonder what medication the chief gearstick thread cutter was on at the time. Roger None - that’s the problem ........ Quote Link to post Share on other sites
BlueTR3A-5EKT Posted January 11, 2021 Report Share Posted January 11, 2021 You could spend a while searching here... https://www.gewinde-normen.de/en/iso-coarse-thread.html Could be M11 x 1.25 which is closest I can work out to 7/16 x 20 I agree the standard TR gearstick threads are 7/16 x 32 ME for sidescreen cars with the straight stick and 5/16 UNC x 18 for the bent stick on wind up window cars. The Stag Innsbruck bent stick for overdrive switched knob is different again. (Unless it is my sidescreen car that has a bent but truncated TR5 gearstick that I turned to size & threaded 7/16 x 32 ME.) Miles, unless you have just had your gear stick re-chromed why not request one on here? I will check my own stock for you. - could turn out cheaper than a special cycle thread tap. Cheers Peter W Quote Link to post Share on other sites
Lebro Posted January 11, 2021 Report Share Posted January 11, 2021 Why not run a 7/16"UNF die down the gear lever, & a 7/16"UNF tap into the the gear knob, then it must fit. I am persueded that my original gear lever was 32 TPI, & I re-threaded it to 20 TPI to match the Saloon knob (which in the end I did not use) Bob. Quote Link to post Share on other sites
MilesA Posted January 12, 2021 Author Report Share Posted January 12, 2021 Oh dear. I hadn't intended to stir up a hornets nest; rather just report an odd thread on my gearstick - probably applied by a PO. Like most others, my understanding was that the thread on a 3A gearstick was 7/16 x 32 ME. My replacement 3A knob presumably has that thread but did not fit which is what started my quest. So last night as part of my daily exercise I walked to the lockup to reconfirm the physical evidence. There is no chrome on the gearstick thread in fact quite a lot missing along the whole stick! None of the following would fit: 7/16 UNF die, 7/16 UNF and UNC nuts. The only nut that slipped on easily was the 7/16 x 20 tipi British Cycle Thread nut I had bought. So I think it is clear that 7/16 x 20 UNF is not compatible with 7/16 x 20 tipi British Cycle Thread. As the evidence suggest and Roger speculates there is something slightly different about the two. Interestingly I have had an exchange with the specialist nut supplier. Even he thought 7/16 x 20 UNF was compatible with 7/16 x 20 tipi British Cycle Thread nuts he supplied but he later confirmed having tested them that there is a difference. Overall not a big deal but an interesting insight into the wide range of engineering standards that evolved over the past 150 years in order to confuse an bewilder us desk jockeys: Whitworth, SAE, UNF, UNC, ME,BSC and so on. Peter thanks for the offer as ever. The choice is to run a die with the correct thread on the gear stick as Roger suggests or rethread the gear knob. If the tap I have ordered is correct I think I will I have a go at filling the knob void with JB Weld and tapping it. If I cock it up - always a high risk in my case - I will not have done to much damage! As for how it got threaded in this way - who knows: Friday afternoon car or more likely a careless PO. Anyway, thanks for all the interest as always. Miles Quote Link to post Share on other sites
RogerH Posted January 12, 2021 Report Share Posted January 12, 2021 (edited) Hi Miles, as mentioned - the UNF thread has bigger/deeper threads (tip to core) than the Cycle thread (shallower) so this would stop the the UNF running down. The CEI20 thread is non standard, and having a much shallower thread depth allows a hole down the middle of the shaft to be slightly bigger than that allowed by the UNF equivalent. This is a good table All Threads Roger Edited January 12, 2021 by RogerH Quote Link to post Share on other sites
BlueTR3A-5EKT Posted January 12, 2021 Report Share Posted January 12, 2021 (edited) Just to throw some more in the mix.... I went through my ME taps and dies today (as you do) and found a die marked 7/16” x 20 ME. So that’s a weird one. It confused me as I thought I only had 7/16” x 32 ME. Peter W Edited January 12, 2021 by BlueTR3A-5EKT Quote Link to post Share on other sites
RobH Posted January 12, 2021 Report Share Posted January 12, 2021 Very odd Peter, I was under the impression that ME threads only came in 32 or 40 tpi. None of the tables I have list a 20 tpi ME thread. Quote Link to post Share on other sites
RogerH Posted January 13, 2021 Report Share Posted January 13, 2021 there is also 26tpi in ME (like the 20tpi) but is not standard. Roger Quote Link to post Share on other sites
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