drop bar

1. n. [Perforating]
A heavy steel bar that is dropped through the tubing or running string to fire the percussion detonator on a tubing-conveyed perforating (TCP) gun assembly. The drop bar must be capable of falling through the string with sufficient speed to impart the necessary force for detonation. Therefore, this method of firing is best suited to vertical or slightly deviated wellbores where there will be minimal drag or friction effect.