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[Alan R]

OR---- have they a suitable Tap or chaser that you could rent / borrow... ??

[Adrian]

Couldn't you just ask our hosts to replace the faulty items with a good pair?



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[PeteF]

Hitchcocks are very good at replacing faulty items and they do sound faulty.

[Adrian]

Found a fork spare plug in the garage and checked the thread against the thread file, it's 16 TPI. Diameter of the threaded section as far as I could tell, 11/16". Any help?



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[Alan R]

Hi Guys-------- new one on me I must admit..It would appear to be a UNS thread....Of the same form ( 60 degrees ) and family of Unified threads but with more TPI than it's matching diameter "cousin" so to speak.......Have a look at this for more info}--------------------- http://bbs.homeshopmachinist.net/thread ... NS-threads ----

And here's a supplier of taps and dies}----------------- https://www.tracytools.com/taps-and-die ... 6-x-16-tpi

[stinkwheel]

Cheers guys.



Sounds like it's a pretty strange thread. I think I'll take them down to my engineering mate and see if he's got any taps that'll chase them through. He might even make me up a chaser on his lathe if it's truly oddball.

[stinkwheel]

Ok, sneaked in past on my way home and he reckons while it's badly cut, if it's not an M18x1.5, it's close enough to run a thread chaser down it. This is great because it appears this is the thread many lambda sensors take and there are LOADS of fittings to chose from, including specific thread chasers and blanking bolts with built in o-rings and socket heads.

[Alan R]

Hi Stinkwheel--------- yes, you might just get away with it..........According to our ADRIAN it's 16tpi.....Therefore the pitch = 1/16" which is}--1.5875mm ( 1.59mm corrected to 2 decimal points).....My gut feeling is that for a short length that slight difference in pitch won't make itself felt....Any longer however and I'd expect to see some shavings coming off the thread flank.....At least the thread angle is now known to be the same at 60 degrees....I'd ask your mate to turn up some test pieces in "Alooominum" or a hard plastic first before committing to the actual job....

[stinkwheel]

Just an update. The fork plugs are indeed M18 x 1.5 which is the same as some lambda sensors. I have chased them through and fitted two blanking plugs with a large allen socket head and built in o-rings which actually cost less than the "proper" plugs. They looks neat and are much easier to fit/remove with an allen key than trying to put them in or out with a jumbo screwdriver.

[Adrian]

I had a look at on-line at the BSW and BSF thread dimensions, and while 11/16"is a recognised though now uncommon size, neither of them are 16 TPI, nor is there a comparable BSPP thread.



M18 is a possibility, though why would Redditch have used that back in the 50's, assuming Redditch fork top plugs and those fitted to pre-plain top Indian forks have been interchangeable all these years? Apart from spark plug threads I can't think of any metric threads that would have been used by Redditch back then. 11/16" is very close to 18mm, 1/16" as in 1/16 of 16 TPI is again close to 1.5mm. As Alan R was able to find actual 11/16" x 16TPI taps and dies listed for sale, my money is on Redditch using a thread of their own choice, which by happy accident is "close enough" to M18 x 1.5mm! I am open to evidence to the contrary...



Of possible interest.



http://www.tap-die.com/contents/en-uk/s ... %20x%201.5



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