TRUMBULL SEALED FLOOR BOXES are ideal to prevent fluids from penetrating the floor slab from either direction. Top side is sealed by an o-ring, and the bottom side can be sealed by use of optional packing gland. Overall length is 11-1/8″, but the underside is tapped to accept 2-1/2″ NPT steel pipe nipples for floors thicker than 11″. When it’s necessary to convert a Floor Box to thicker floors, use a 2-1/2″ pipe nipple, 1/2″ longer than the increase required, as the threads on the underside of the Floor Box are 1/2″ deep.