Charlie,
I have been looking at this myself, in order to 3D design and print some. The Haynes manual describes them at trapezoidal which seems to be supported by photos. The manual also contains a photo showing the features on the 2 metal plates either side - something I’d not spotted previously so back to the CAD!
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Regards TeeELL
Growing old is compulsory, growing up is optional.
I did have thought a while ago that the unditching beams were cut down from a larger baulk of timber. In WW1 heavy timbers were (I think) considered a strategic resource possibly a hangover from the days when Naval ships were wooden. It should be possible to estimate how large the piece of timber was that the beams were cut from. I wouldn't be surprised if the large timber was some standard size like 1 foot x 6 inches. As usual I got distracted and never got back to it.
