Hi Mike
If I recall correctly 10mm was an option for very heavy units, at extra cost. My shelves are at most 8mm and 6mm respectively, but sufficient for the loading in my application.
For a very heavy power amp 10mm would be advised. I think 10mm shelves may have been specified as standard on much wider units where more than 1 unit could be placed on 1 shelf.
10mm is standardised Marketing Blurb and misleading.
Hector

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