I've never had aluminum stock this thick before...
It sits right at 3.07mm, according to the caliper. At that thickness, I won't have to radically adjust the date-dial of the polar-scope via its retaining-rings, like I would've with the old spacer; perhaps only very little or none at all.
The old spacer sat at 3.37mm, incidentally.
If I'm careful in laying the spacer out on the sheet, I can probably get a total of three spacers out of it, in case mistakes are made.