All a-51 Fixtures Are Factory-Sealed, No External Sealing Fittings Required; New High Temperature Phenolic Connection Block in Mounting Hood Has Rugged Leaf Spring Contacts - Loosen Two Screws, Rotate and Remove for Quick Wiring; Safe, Easy Servicing or Re | Explosionproof, Dust-Ignitionproof; Smooth, Rounded Integral Bushing in Each Hub Protects Conductor Insulation; Accurately Tapped, Tapered Threads for Tight, Rigid Joints and Ground Continuity