Why are gauge measurements between aluminum and steel different? For instance, 10 gauge aluminum is .1019" and steel is .1345" ?
My McMasters-Carr catalog shows the differences, but makes no attempt to explain why.
This page shows 10 gauge wire (AWG) is .1019" and linked from that page, this one shows 10 gauge rolled steel is .1345".
The difference in standards is not so much between steel and aluminum as it is between ferrous and nonferrous products. Since early ferrous and nonferrous products were likely produced by different manufacturers, they probably developed their own arbitrary thickness standards independently and never reconciled.
Also, some nonferrous sheet metal suppliers don’t use any “gauge” thicknesses. Instead they use “preferred” thicknesses, with some of the more common ones being 0.025", 0.040", 0.050", 0.100" and 0.125".