Letter / Number Stencil Sheet A4. Stencil size : A4 ( 297mm x 210mm ). Reuseable Stencil of Capital Letters & Numbers. 20mm (2cm) / 25mm (2.5cm) or 30mm (3cm). The stencils are made from thin Mylar polyester sheet - 190 micron (0.19mm), a very strong type of polyester sheet that allows for acute bending and manipulation.