The MGA With An Attitude
FASTENERS with Odd Threads - CF-104

At 01:11 PM 6/6/05 -0600, Will DeDalis wrote::
>"Is their a list of Whitworth used on MGA and B, brake abutment, crank pulley, front wheel hub nut?"

There are precious few Whitworth fasteners on the MGA (maybe none), and even fewer on the MGB (also maybe none). Most of the threads were standardized to Unified National thread standard during WW-II, and MGA design and production came later. Most threads are UNF (Unified National Fine), functionally interchangeable with SAE standard threads. Some threads in soft castings are UNC (Unified National Coarse). In the aluminum gearbox the bolts for starter motor and remote shift extension attachment were coarse thread for early cars and fine thread for later cars. For some double threaded studs the bottom end will be coarse threaded and the top end fine threaded. This has a functional purpose to allow the nut (shallow ramp angle) to be tightened while the stud (steeper ramp angle) does not turn (cylinder head bolts for instance).

Screws in the Auster windscreen assembly are British BA series, mostly 2BA for the smaller ones (although some intermediate aftermarket service parts may have #10-32-UNF threads).. The wing bolts to secure the top frame to the windscreen are 5/16-22-BSF (British Standard Fine). Some small screws in the SU carburetors may have BA standard threads, maybe also the wiper motor. The starter pull switch, starter input post, control box and fuse box grub screws are all BA series, which appear to be inch size but with an odd pitch. All of those applications are a holdover from designs and parts in production which pre-date WW-II. Some threaded plugs in the sides of the engine block and oil pan may appear to be 12mm, but are actually BSP(S) (British Standard Pipe, Straight threads). Side fill and bottom drain plugs in gearbox, rear axle, and fuel tank are tapered pipe threads.

You do not need any metric or Whitworth wrenches for the MGA. I have never owned a single Whitworth wrench.

However, .... Some recent production aftermarket hydraulic hoses have metric dimension wrench hex fittings (what we get for having them made in a foreign country). Not long ago I received from Moss Motors a set of clutch cover to flywheel bolts with proper 5/16-24-UNF threads but 12 mm hex head. These apparently had the 5/16 inch threads cut onto a standard 8 mm screw blank. Close, but no cigar. This disturbs me to no end when I have to find a metric wrench to work these non-standard fasteners, even though I bought them from a reputable British parts supplier expecting original specification.

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