Hitchcocks Forum

Could somebody please tell me the tread and size of the 16 rocker cover nuts on a constellation?

Thanks,

Rasp.

Don't know, but they almost certainly Cycle Threads (BSCY) with a thread form t 26 TPI. Best think is to speak to our hosts, or take one off and try a Cycle Thread bolt in it. Beware if it is 5/16 diameter then a 5/16 BSF thread is also 26TPI.......but the thread form is different.

If they are the same as the Bullets they'll be 1/4 cycle. You'll get away with 1/4 BSF as the difference is only the pitch of the tread BSF being 55 degrees to cycles 60.

That is awful workshop practice Simon. However, as there is not a lot of torque on those nuts and they will not be disturbed very often, you would probably get away with it. Much better to get the correct thread though.

You'd really hate my using 8mm x1mm as 5/16x26 then. Works a treat but!

Peter, near impossible to get those cycle threads out in the Collonies we have to order them from MrH and apart from the waiting time P&H is often more than the cost of the item

Hi SIMON---Just me being technically pedantic but the angle of the thread is NOT the pitch ( this being the distance from one place to the next identical place for a single start thread, usually measured at the top or crest of the thread)..........

Alan is perfectly correct. the pitch is usually quoted as TPI (Threads Per Inch) or in the case of metric threads in particular the actual dimension from oe thread crest to the next. It is also, obviously, the distance that a nut will travel in 1 revolution e.g. 1mm. The urban myth about 1/4 diameter BSCY, BSF and any metric bolts with 1mm pitch is that they will function correctly. The thread angles on the first 2 are different and so the male and female threads will not mate correctly. This can result in failure when tightening, seizure and thus stripping if any corrosion takes place or if overtightened. The clearance between the crests of the bolts and the mating depths of threads in nuts can also cause problems if you try to mix thread forms. BSCY threads are available in the UK from a number of suppliers including Acme Stainless (Google is your friend). I am sure many will simply try and fit mis-matching threads but that way lies disaster eventually. If you use stainless fasteners also remember Copper Slip will prevent any pick up and subsequent siezure, but bear in mind the effect that its lubricating quality has on any torque settings. HTH.

Yes Alan you are of course correct, I hang my head in shame. However as Norm says good luck finding a supplier of anything but 1.25 metric in any quantity out here in the Southern Hemisphere. We hunt down Whitworth hex bar like gold prospectors and have to manufacture most of our nuts and bolts if we want anything approaching originality. What it does mean is that when restoring something important there is no horrible nylock stainless all over the place. Washer faced Whitworth hex with real cadmium plate (for added health) is the gold standard here. However precious as one can get over thread angles and the difference between 25.4 and 26 tpi the fact remains that a nice fresh nut tightened up with a split and flat washer is going to be better than and old shagged one any day. Sometimes needs must. I draw the line at a tight fit or a graunced thread but when they spin on and don't wiggle ...oh and in the case of metric fine 8mm they have a 13mm hex which is passably close to 1/4 whit I'm a happy camper.

Norm, I appreciate your difficulties. Even it UK I almost always get odd fastenings on Ebay. Might be worth a look for sourcing stuff like this out there.

As a case study, I recently wanted some odd bits for a vintage Farrari two-wheeled tractor. After much searching I finally went to Ebay (Italy) and there they were - hundreds of them (and P&P was much cheaper than I would have thought)
The internet has made getting just about anything you want much, much easier but you still need to know where to look (or get lucky)