16 CFR § 1507.3 - Fuses.
(a) Fireworks devices that require a fuse shall:
(1) Utilize only a fuse that has been treated or coated in such manner as to reduce the possibility of side ignition. Devices such as ground spinners that require a restricted orifice for proper thrust and contain less than 6 grams of pyrotechnic composition are exempted from § 1507.3(a)(1).
(2) Utilize only a fuse which will burn at least 3 seconds but not more than 9 seconds before ignition of the device.
(b) The fuse shall be securely attached so that it will support either the weight of the fireworks device plus 8 ounces of dead weight or double the weight of the device, whether is less, without separation from the fireworks device.