Thread differences

[a101960]

What is the difference between BSC and BSF threads? All of my spanners are marked as being BSW, BSF or BA. I know that BSW threads are a course thread form, and are typically used where a stud or bolt is screwed into ally castings etc, and that BA is most commonly used in electrical equipment. What I am confused about is the differences between BSF and BSC. The reason I need to know is because I want to clean up some of the threads on some of my studs, and I need to know what dies to get.
John

[terryg]

Try http://www.britishfasteners.com/threads/bsc.html it might help answer your question.

[Derby Rob]

hi,
    they are not the same. but i think you will find most of the nuts/bolts that are used to hold things to or on the frame are bsc,and anything that screws in to the engine alloy is whitworth.But having said that i found the odd unf bolt on my 61 a7!
 

[duTch]

 What Rob and Terry said, and as far as I know there should be no UNF anywhere....
 Think the maggy gear and genny sprocket nuts are BSF, and the Head bolts.
 
The thread angles are different 55˚ & 60˚, but I never remember for sure which is which..
BSC fine is all 26 tpi, and BSC coarse I think is 7/16" up @ 20tpi..?

[Topdad]

Hi Dutch, I wouldn't say anything was definate in '61 re the a7 ,last year in production or pretty close BSA would have been raiding parts bins to finish off bikes from what was held on stock and sure I 've heard of other anomolies as well of course PO's would have had some input as well ,cheers Bob

[duTch]

 Yo Bob, I thought that about the later 10/7's after I posted....chose to disregard PO mods., and stick with what they were (likely) originally made, but figured not UNF...till later...unless maybe for US models...??

 I was aware the A65/50's had started to go UNF (or was it BSF in some casings?), but also chose to stay away from that...and leave it for those who know

[BSA_54A10]

Head sizes on CEI/BSC are the same as BS ( one size smaller than BSW )
The thread is a very fine & shallow one with a shallow depth designed to resists vibrating loose.
Pitches are fixed usually 26 TPI or 20 TPI as in most cases they were cut into a part using a thread tool in a lathe and not a tap & die.
Do not use BRASS taps & dies while they are the same TPI the thread is deeper and will cause the fittings to be loose.
The same applies to using 1/4 BSF in place of 1/4 CEI.
Also be carefull if you buy a set of CEI taps & dies.
A lot of the threaded lugs were forged so are too hard to run a high carbon tap down, you really need to fork out the extra for the tool steel ones.
Break off a high carbon tap in one of these and you are in for long relationship with a dremel tool and diamond burr.

[a101960]

Thanks for all your comments chaps. On balance I think that maybe it will be much simpler to by new studs.
John