The PocketWizard AC57 is used with the PocketWizard AC7 HardShield. It fits into the high-power terminal of a Canon 580EX or 580EXII and redirects the power cord of an external battery pack back and away from the antenna of the PocketWizard FlexTT5. This provides the best shielding against RF noise and greatly improved working distance and operation of the FlexTT5 when used with an external power supply. As the adapter mirrors the fit of the Canon flashes, it can be used with any Canon- compatible external battery pack.