Threads...

hello
you are partly correct on the aluminium threads, although although there are odd occasions when British cycle threads are used. Lighter steel parts use British cycle (26tpi) and heavy steel and cast iron use another cycle thread 20tpi. Presently I use UNC for these parts as they are almost identical.For electrical components tend to be BA threads.
Hope this helps
regards
Andrew

Get yourself a couple of thread gauges. Early machines (pre AMC) depended on BSCy threads into castings etc. ( often 5/16" BSC), a good fine thread but is easily confused with BSF if you are not aware.  If other thread bolts have been used you need to be careful changing back to original as much of the material will have been destroyed.  For internal threads it is wise to produce some wooden inserts that you can wind into the holes to leave a witness mark on the wood and measure that with your gauge. Thread form and thread angle also differ between  same pitch threads so get yourself a Zeus notebook or similar to understand the differences. Steer away from stainless, it is hard, sharp and does not hold when subjected to vibration as a steel bolt would.  Electrical items often use BA thread forms. All will be seen in the Zeus ( or similar) engineers note book.

Hello again
Must have had a senior moment in my first reply, I said UNC, should have been UNF, also buying a thread gauge will be money well spent.
regards
Andrew

... aren't "near enough" in my experience at 28 tpi and 26 respectively. Ask any Commando owner who's put the wrong nut on the stud coming down at the back of the head between the inlet ports!

I see no point in using the wrong threads when the correct ones are very widely available, although I agree that UNC and Whitworth are pretty near in many cases apart from the thread angle. At least no-one is suggesting metric. Not yet anyway......

Hi all,

   The compatibility between these is only with larger sizes 7/16"  1/2"  20tpi  which are used on engine bolts, fork yokes etc.with hexagon head sizes being different. Just try clean threads by screwing in by hand, you will soon realise if it's wrong. Wikipedia has some good info on pitch and angle forms. Norton didn't use many BSF threads at this time, but there are anomalies such as headlight main bolts, double check everything and assume nothing.

Stick to what was originally there. Once you start substituting UNF for Whitworth you are going to need AF spanners as well as your Whit/BSF spanners.
One of my pet hates is having to unfork previous owners' nut an bolt bodges.

The threads I would expect to potentially find on an ES2 - 

BSF
BSC
Whitworth
Whitform
BSB somtimes called Whitform, but not always. 
BSP

In the past two months I have encountered 2x Commando cylinder barrels damaged by using incorrect stainless fasteners and 1 x Commando cylinder head damaged by stainless fasteners, not so much the fasteners being stainless but the incorrect threads on them.