this was not my idea, i found it on youtube.
WARNING: while using a Flash Grenade, it is a very good idea to wear non-flammable gloves, and sunglasses.
DISCLAIMER: If you end up hurting yourself or others or setting something on fire, then I take no responsibility for it.
Step 1: Materials
Two cigarette lighters, (a small bic one is fine)
the other one is to heat the flint up.
Step 2: Destruction!
It should look like the second picture.
Step 3: The barrel
Step 4: The Flash itself
Strech the spring so its relatively long, then wrap it around the flint.
CAUTION: make sure that the flint is very secure in the spring so that when you pull your arm back to throw it you don't end up setting your pants on fire.