The plastic templates, Gem-Temp J-345, features marked common millimeter sizes of ovals and circles used in designing cabochons. The plastic templates allows you to see the complete slab for the best pattern for the cabochon. The oval patterns are sized from 10mm x 8mm up to 40mm x 30mm. Circle patterns are sized from 7mm up to dollar size or 38mm. The templates will greatly aid in correct sizing for placement in popular sizes of jewelry findings. A millimeter scale is also shown on the bottom of the templates for measuring.