Spolette

From pyroGuide.wiki

A spolette is a delay fuse consisting of a hollow wooden dowel or a paper tube rammed full of black powder. A spolette is glued into the wall of a fireworks shell and ignited by the lift charge that launches the shell into the air. The spolette, after a delay that allows the shell to reach its top of trajectory, ignites the shell's main effect(s). The tough wood construction ensures that the fuse burns reliably despite the explosive force and acceleration of the launch.