Piercing Saw
From DT Online
Piercing saws are a type of framesaw used in jewellery and similar fine work, to cut intricate shapes out of sheet materials such as silver.
Very fine teeth blades are clamped and tensioned within an adjustable frame. They face towards the handle because they are used by pulling vertically down against a V Board as shown.
Note: To cut internal shapes, small holes are first drilled in the material through which to thread the blade