Rudge-Whitworth pattern knock off spinners are made commonly in 32, 42, 52 mm sizes (and larger), as well as in both coarse and fine threads, either 8 or 12 threads per inch. Knockoff nuts are made in two ear, three ear, and octagonal drive variations. Material can be either steel or brass (both chrome plated). There are subtle variations in shape of the front face and shoulders and face markings. All MGA (and MGB) use 42-mm series hubs and nuts, but the thread changes from fine to coarse.

Generally speaking the knock off nuts are interchangeable between applications as long as thread and diameter match, but there is one notable exception. That is the Dunlop steel or alloy peg drive wheels. These wheels were used on the Twincam, Gordon Keeble, Jaguar D type and lightweight E type, as well as racing derivatives like the Lister built cars. The Gordon Keeble uses the same parts as the Twincam, but have not verified a D type part for measurement and comparison. They use a 5 peg rather than 4 peg wheel and the concern is that as in wire wheels, they use the larger 52 mm rather than the 42 mm size.

The difference between the normal Dunlop wire wheel spinner and the Twincam steel wheel version is the taper of the inside of the knock off and the outside of the wheel. You can NOT interchange these or you will have a single point contact area on the spinner which will be insufficient to safely retain the wheel.

"The outside diameter of a MGA wire wheel spinner is 3.180"
The outside diameter of a MGA Twin Cam (or Duluxe) spinner is 3.350"

NONE of the aftermarket spinners are safe for use on a Twincam or Deluxe unless they have the correct angle and are stated to be suitable for Twincam.