5“ pin-end scroll saw blades
Scrollsaws are typically used in one or more of the following circumstances:
Cuts are in the interior of a workpiece (holes). In this case, you would typically drill a hole big enough to feed the scrollsaw blade through, then reconnect the blade, make your cut, disconnect the blade and pull it back out of the piece.
A very clean cut is needed. The scroll saw tends not to produce a lot of blowout (splintery cuts). By contrast, the jig saw, which would be a comparable saw in many regards, tends to produce very rough cuts.
Very tight curves are needed. Scroll work is a science/art in and of itself. A whole field of woodworking exists around scroll saws and their handtool cousins, the fret saw. These are usually intricate, ornamental pieces. A scrollsaw will cut a tigher curve than either a bandsaw or jigsaw.
The manual for this tool, including directions on changing blades, is here.