Hanging dissimilar items in same frame for hot dip galvanizing

A. This is a good question for galvanizers. I think it depends on the style of operation. Some plants have the same material all the time, from a small number of customers, perhaps even their own manufacturing, and so jigging becomes much more uniform.
But others (like us) are "jobbing" plants, where the material is very varied in shape, thickness, cross section etc. Some solid steel, some hollow sections, some mixed.

The jigging then becomes a compromise:
If you separate all material into similar thickness, and separate hollow from solid, you will surely get more consistent, and more controllable coating thickness, immersion times, pickle times, etc. But you risk loosing the traceability (identity) of the pieces of steel from each customer.

If you keep each customers work together (recognising that it will be a mix of all manner of material types) you get better traceability, but more variable performance.

There's some middle ground between these two. Where larger orders of similar material are available, some separation is possible. Where a customer has easily identifiable pieces, they could be mixed with other customer's work.