Right, found it!
Imperial is most relevant to all dimensions.
Thread diameters 3/16″, nuts 21/64″, hole 3/16″, thickness 1/4″ , step 1 1/32″ and step 2 1/16″
No visible numbers on the part itself.
The one hex head bolt has ‘LL’ on the head.
I’ve mislaid my calipers so can’t measure threads at the mo.