MG MGA Twin Cam Workshop Manual page 22

Identification has been standardized and is effected in the following manner:
Nuts. By a circular groove turned on the end face of the nut or by connected circles stamped on one flat of
the hexagon.
Bolts and set screws. By a circular depression turned on the head or by connected circles stamped on
one flat of the hexagon.
Wheel and nuts. By a notch cut in all the corners of the hexagon.
It is of the utmost importance that any nuts, bolts, or set screws marked with the above identifications are
used only in conjunction with associated components having Unified threads and that only replacement
parts with Unified threads are used, as these are not interchangeable with Whitworth, B.S.F., or Metric
threads.
The Unified thread is, however, interchangeable with the American National Fine (A.N.F.) thread for all
practical purposes.
This illustration of the Unified thread and the A.N.F. thread to the same scale indicates their close
relationship
Spanners. It is to be noted that all A.N.F.- and Unified-threaded nuts and hexagon-headed bolts are made
to the standard American hexagon sizes and that spanners of the appropriate size must be used when
tightening or loosening them.
KEY TO SPANNER SIZES (Nominal widths between jaws)
NOTE. —In the case of some Unified-threaded components the size of the hexagon for the nut is different
from that of the bolt. Where this occurs the spanner size is shown in heavy type in the above tabl
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