 Requirements for a hand grenade fuze are defined by the projectile's small size and slow delivery over a short distance.This necessitates manual arming before throwing as the grenade has insufficient initial acceleration for arming to be driven by "setback" and no rotation to drive arming by centrifugal force.Aerial bombs can be detonated either by a fuze, which contains a small explosive charge to initiate the main charge, or by a "pistol", a firing pin in a case which strikes the detonator when triggered.