Starting in 1916, plates were made of steel, and approx. 15 x 8 inches in size.
After reaching 99999, an A prefix was used in 1916, and then, for a very short time, an O prefix was apparently used as well.
Apparently, the painting process was not very precise on this first embossed issue, so some of the more poorly painted plates were touched up before distribution.
Because of this, some 1916 issues will have "natural" brush strokes on the numbers, applied during the manufacturing process.
1916

1916

1916

1916

1916Allan Attanasio

For 1917, A, B, O, X, and N prefixes were used.
I'm not sure of the order in which these were issued, except that the all-numeric plates came first.
1917

1917

1917

1917

1917Leib Brothers

1917Leib Brothers

1917

1917Leib Brothers

After going to 6 digits in 1918, the alpha prefix was no longer necessary and all-numeric plates were issued until 1925.
1918

1918Dave Zullo

1918

1918

1919Dave Zullo

1919

1919

1920Dave Zullo

1920

1921John Anshant

1921

1921

1922John Anshant

1922

1923

1924Leib Brothers

1924

1925
