Handlbar clamp bolts thread size?

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

It might be M8, small difference in diameter and pitch to your measures.

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.

On my roadholder forks the handlebar clamp screws are 5/16" bsf.

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. 

John,

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

Philip

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

" 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.

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.

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

.........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

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.  

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!

Wishing to change mine on my Vin. Definitely 28 tpi. Thread od is 0.204 inches.

They have to be 7/32 inch BSF. OD for that is supposed to be 0.218 inch. Probably just a bit worn, I guess.

Trev

Anna is usually right about Bikes built by Norton.   AMC  went thier own way . with changes for no apparent reason.

I have been checking out the DSNs with regard to the original question about handlebar clamp bolts. Strangely, these agree with Anna in respect of being 5/16" x 26 tpi.  However, cross referencing with suppliers and checking my own spares box, I find them to be as first mentioned in this thread as 5/16" BSF x 22tpi x 3/4".  With Part Number 19437.  These being suitable for Roadholder forks when used with recessed half clamps.  A slighly longer version with reduced Hex heads but same threads appear to be for the earlier Nortons.

Norvil sell the 19437 screws (bolts) but also list a similar part as 016947. But in my spare parts list these are shown with 5/16" x 26 CEI threads.   RGM list them as P/N 067745H with threads of 5/16" BSF x 22tpi x 3/4".

Adding to the confusion......a further mention is made that such items changed their threads to 5/16" UNF on the Commando.  I wonder what the Mercury used or was that answered above?

Andover do their usual thing of showing a photo & two numbers, for the part, but no mention of the threads.

I don't recall Posi being around in the1950s or early 1960s at least.  I've always understood that they are a European invention and Phillips are USA - also used by Japan.

Orriginal chaiguard fixings on the 59 built  DL's were   posi (or phillips!) .  Not sure but I think the rear number plate fixings were too . I had a very standard DL back then.