Mill sheet is an untrimmed piece of pewter just as it appears after the final
rolling mill pass.
The edges are unfinished and not perfectly parallel, and the ends are neither straight nor perpendicular to the edge. Thicknesses across any dimension may vary +/- 0.002", and the widths and lengths available vary depending on thickness. Quoted dimensions are nominal values; Lengths will vary somewhat from sheet to sheet. Pewter in these sizes is not perfectly flat initially, but will achieve flatness with time.
This form is mostly specified when maximum dimensions are required, such as for a countertop, or when the final size of the sheet is undetermined.
See our Mill Sheet Dimensions Chart (PDF) showing the dimensions available at various thicknesses.