Jigsaw Blade
Do not use blunt blades, as this will require extra pressure, possibly resulting in blades snapping while in motion. Always use hand, eye and breathing protection when cutting material with a jigsaw or other power tools.
Blades for jigsaws have different fittings (determined by the shape of the blunt end) and different purposes (determined by the thickness and the blade pitch, which is the distance between the teeth).
Blades designed for wood have fairly large teeth that are spaced typically around 3-4mm apart. For cutting metal and plastic, you will need a thinner blade with tiny teeth and lots of them, spaced typically <1mm apart. Although there are many types, there are the most common.
If in doubt, read the box the blade came in (assuming the text on the side of the blade has rubbed off). And see the Jigsaw Profile for more information.