These corrosion-resistant outlet boxes provide access for maintenance, allow the connection of different lengths of conduit, and for changing the direction of conduit. GR, GRF, and GRTS explosionproof, dust-ignitionproof outlet boxes are manufactured with accurately tapped, tapered hub threads for tight, rigid joints and. Get 30 days to pay with Net 30 Terms. Your feedback is important to us and is greatly appreciated. They are suitable for Class I, Div 1 and 2, Groups B,C,D: Class II, Div 1 and 2, Groups E,F,G;.