The MGA With An Attitude
THACKERAY Double Coil Spring Washers -- UT-129
Thakeray washers seem to be somewhat elusive, as I spent considerable time searching the internet to find just one picture of the little creatures. These multi-coil spring washers look like a short section of a flat wire die spring. They will have slightly more than 1-3/4 turns in the coil. Cheap ones will look a lot like the picture. Better quality ones would have an offset in the coil half way through equal to 1X thickness of the wire so when compressed to solid height it will lie flat with two layers of metal only.
They are used in a few places on the MGA, but seldom seen. There are a couple of them (5/8" bore and rather thin) on the engine rocker shaft to secure the front and rear rocker arms. Another common application is 5/16" bore as part of the flex mount for carburetors on the MGA Twin Cam. When used for flex mounting carburetors you want the better quality parts, as they need to be set to a specific compression (0.040" between the coils). The cheaper simple coil ones would not lie flat and will be higher stressed. The active vibration means there will be many millions of spring cycles that tend to fatigue the metal leading to broken washers.
This list comes from Moss Motors USA with some sizes available. The drawing here is not exactly correct. The center coil should have an offset smaller that that shown, and the top and bottom surfaces should NOT be flat and parallel in the free state. I have not seen any of these parts form Moss to verify the shape (good or bad).