A piercing saw is a type of saw

Saw

A saw is a tool that uses a hard blade or wire with an abrasive edge to cut through softer materials. The cutting edge of a saw is either a serrated blade or an abrasive...

 commonly used in jewelry making on sheet metal

Sheet metal

Sheet metal is simply metal formed into thin and flat pieces. It is one of the fundamental forms used in metalworking, and can be cut and bent into a variety of different shapes. Countless everyday objects are constructed of the material...

. It is usually used on softer metals as the saw is delicate.

A piercing saw is shaped like a smaller coping saw

Coping saw

A coping saw is a type of hand saw used to cut intricate external shapes and interior cutouts in woodworking or carpentry. It is widely used to cut moldings to create coped rather than miter joints. It is occasionally used to create fretwork though it is not able to match a fretsaw in intricacy of...

. The blade is held in tension in a metal frame. The frame throat size can range from 50 millimetre.

Saw blades come in many different thicknesses and your blade selection will depend on the material being sawn and nature of the work being done. For very fine delicate work, and for cutting very thin material use a finer blade, and for general purpose cutting a heavier blade. Saw blades have a range of sizes, from finest to coarsest: 8/0, 7/0, 6/0, 5/0, 4/0, 3/0, 2/0, 1/0, 00, 0, 1, 2, 3, 4, 5, 6.