More about steel speaker grills:-
The sheet I use most is 1.5mm thick mild steel, with 4mm perforations and an open area of 60%. This probably accounts for 90% of the grills I produce. There is an alternative sheet which is used for heavy duty applications, still 1.5mm thick and 4mm perf, but the open area is just 40%. The heavy duty sheet is 50% heavier and obviously much more robust. There is a downside in that you do lose about 1.5dB from the top end (above 10kHz) although most people wouldn't even notice. Unless you specifically ask about the heavy duty sheet any quote will be for the standard.
As a comparison here's (below) a picture of the 2 grills side by side. The standard sheet is on the left:-
Here's (below) a picture of a "Box pan" grill (folded returns on all 4 sides):-
I cant stress this enough, please measure the aperture EXACTLY, don't make any allowance for fitting. When I cut the grills I have to work to the perforated pattern. I will always cut under-size on the basis that if it's 1mm undersize it's a perfect fit. If it's 1mm over size it don't fit at all. Give me the exact aperture dimensions and let me make the fitting allowance