Regardless of their size, wheels all have the same features as shown above.
Drivers: These contain gunpowder and the sparks emitted from these drive the wheel around. Some wheels hide the drivers behind packaging. Note: Some very small wheels have a spiral tube filled with gunpowder instead of individual drivers.
Fuse: Where you light it.
Free nail: Every wheel should have one!
Mounting hole: This is where you bang the nail through to mount it to a post.
Connecting fuse: Where the wheel has multiple drivers (three on the wheel pictured above), each one will have a fuse linking it to the next one.
Warning label and instructions: The important things you need to know about the wheel, its classification (Category F2 or F3), the net explosive content (NEC) and so on. It’s on the other side of this wheel.