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.
Hi, Andover Norton seem to think they are 5/16" UNF x 3/4"? See link:
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.
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.
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.
My 1969 Mercury has Roadholder forks and the have 5/16" BSF socket head clamp bolts, but this size has 22 TPI.
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!!.
" 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.
Yes probably Phillips on the fully enclosed chaincase. They are pozidriv now!.
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.
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!
Oh dear, that's what I had to use on the Atlas , but at least my old stock is Whitworth!!.
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.
Anna is usually right about Bikes built by Norton. AMC went thier own way . with changes for no apparent reason.
Are more likely to be 1 BA as that is .2087 in dia and 28.25 tpi according to my Zeus book
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.