This stamp may have a rectangular grill pattern impressed into the back of the stamp. These patterns vary in their dimensions, each different dimension receive a classification. These are "A Grill' ''B grill' etc.

The dimension of the grills are as follows
E Grill: 11mm x 13mm, 14 points x 15-17 points
F Grill: 9mm x 13mm, 11-12 points x 15-17 points
Z Grill: 11mm x 14mm, 13-15 points x 18 points (ONLY ONE EXAMPLE IS KNOWN TO EXIST)