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MG TD TF 1500 - Bolts and nuts threads withworth or BSF

Are the bolts and nuts of a mg td withworth or BSF ?? (except engine)
I am very confused. Moss Motors offers BSF tap and dies, but some people tells me the bolts and nuts are withworth . What is the difference ? What should I buy ?
Thanks,
Jose Vicente Vargas

For one thing, buy your taps and dies from British Tools. A lot cheaper.
Tom Maine

The Bolts and nuts are the fine thread Whitworth pattern thread.
This is properly termed British Standard Fine or BSF.
Most automobiles use the fine thread to minimize the accidental unscrewing from vibration. (e.g. SAE, NF, BSF, and fine thread metric)

The coarse thread Whitworth pattern was invented by Whitworth to provide interchangeability of bolts ( particularly for machines and guns.)
He also chose the size of the bolt heads to fit hexagons that could be easily machined from round stock, thus the odd "across the flats" sizes and strange size wrenches.
Wrench size is marked on the basis of the diameter of the bolt whereas the US practice uses the size of the head.
( eg. 1/4 BSF vrs 7/16 both are used for 1/4 in bolts and nuts)
It is normally called Whitworth ( Or British Standard Coarse).

Both BSF and W have the same size bolt heads that require "Whitworth" sized wrenches.

However at some time after the creation of the Whitworth standard the bolt head fir a particular size bolt was reduced by 1/16 in.

Hence a wrench marked 1/4 W fits a 5/16 bolt that requires a 5/16 BSF marked wrench to fit.

So in general All MG's up to 1955 require Whitworth sized wrenches but have BSF bolts and nuts. There is on one Whitworth bolt on a T Car, the bolt that screws into the aluminium front plate of the generator.


Don Harmer

"So in general All MG's up to 1955 require Whitworth sized wrenches but have BSF bolts and nuts. There is on one Whitworth bolt on a T Car, the bolt that screws into the aluminium front plate of the generator."

I might add, that one bolt has long since been replaced with an American National Course bolt in probably 99% of the cars. The Whitworth and National Course bolts have the same thread count (with the exception of 1/2" bolts) and even though the thread profile is slightly different, the bolts can be substituted for one another.

You can download a chart of standard threads that include American, British and Metric threads and was compiled by Don Harmer above by going to the chart, Standard Threads in the Other Tech Articles section of my web site at: http://homepages.donobi.net/sufuelpumps/ Cheers - Dave
David DuBois

This thread was discussed on 12/04/2010

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