RE Hamilcar glider, the material would most likely be DTD166, used in Hawker fishplates and most aero engine exhausts, as it could be work hardened, as well as cut into shape in any old shed. By avoiding the need to heat treat to develop strength, it was cheaper to make a fitting from this than from a ‘cheaper’ carbon steel that needed heat treatment.

Using a thicker carbon steel that would not require heat treatment would introduce weight penalties.
There were many, many firms stamping out Hawker Hurricane fishplates in DTD 166.

The fascinating journey would be to compare Hamilcar plates to Hurricane plates, to see if there are any matches….