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Handlbar clamp bolts thread size?

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Can anyone tell me the thread size of the handlebar clamping Allen bolts. Having measured them as near as I can they seem to be 5/16th dia  20 tpi but that does not appear to correspond with any standard thread size that I can find. 

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Hi, Andover Norton seem to think they are 5/16" UNF x 3/4"? See link:

https://andover-norton.co.uk/en/shop-drawing/498/handlebars-controls

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UNF only came in with the Commando, and M8 never with real Nortons - although who knows what some PO has bodged into place. My 1952 ES2 has 5/16 Cycle bolts.

I don't think socket heads would have been standard on a heavyweight twin either.

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Leonard - Having looked up your reference it says it is 5/16" BSF x 3/4 (NM19437).  I have remeasured and concluded it is 22 tpi my apologies. The technique I use is to put the bolt alongside a vernier gauge and take a photo on macro - than display it on screen and make it nice and big. Then move the vernier digitally and count the threads. Having done it more carefully with a longer bolt with the same thread I conclude it is 22 tpi.

 

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Definitely BSF on Heavy Twins and many other models. P/N and details as below

19437  Socket Head Screw  BSF  5/16" x 22 x3 /4" Bright Zinc or Parkerise finish.

I may be wrong but apart from the rocker feed union bolts and inlet rocker cover stud, I cannot think of any other use for these size screws on a non- Commando Norton. 

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John,

My 1969 Mercury has Roadholder forks and the have 5/16" BSF socket head clamp bolts, but this size has 22 TPI.

Philip

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hello  handlebar clamp bolts should be 26 Tpi  Cycle  thread    5/16ths  thats the ones built in birmingham   anyway    Yours  Anna J   

I recently replaced the allen  screws on the 67 Atlas  as I needed to fit some bar risers to overcome the usual clash between cables and fork nuts. Its worked well  but was not simple as the riser profile had to be fettled to fit and 4 hands (or more) needed to reassemble. I should be able to find out what screws I purchased ,but bear in mind this AMC bike may be different to the real thing ,Norton of Bracebridge St!!. Allen screws and even posidrive screws were fitted to Nortons in 1960 and possibly before. (rear chaincase, Distributor housing,Alternator basket,Top yoke) .Never did find anything to fit the Dissy housing cap screws!!.

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" The technique I use is to put the bolt alongside a vernier gauge and take a photo on macro - than display it on screen and make it nice and big. Then move the vernier digitally and count the threads. Having done it more carefully with a longer bolt with the same thread I conclude it is 22 tpi. "

Why not get a thread gauge (less than a fiver) and do it the easy way?

" even posidrive screws were fitted to Nortons in 1960 "

If cross-headed screws were fitted then they certainly wouldn't have been pozidriv (correct spelling). They'd have been Phillips.

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The other thing about them is that the bolt heads have a reduced diameter compared with standard socket-head bolts of that thread size, in order to fit snugly into the recesses in the top handlebar clamps.

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Oops - sorry John,  can't even copy properly (what a muppet?!). Good that you checked. Anyway - lots of advice from other folks since then to decipher. Good luck.  Len

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.........I think that one will find no Phillips head screws on a Norton, or BSA or Triumph. They are all Pozidriv, including Lucas components.

Mike

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Interesting , I can't be sure as the original (cross head whatever!) went rusty and were replaced by me from my stock of whitworth  construction  fixings. I have a hundred or more.  

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if they were pozidriv but I'm sure you are confident. All my bikes have been well used before I got them so I have no idea what they left the factories with.

What I can be sure is that no manufacturer used 6mm metric roofing bolts with square nuts as a previous owner of my Ariel Arrow decided to do!

 

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