Double branches in a soil stack have a number of uses, but essentially they are used for the purpose of connecting multiple pipe runs, usually in a vertical plane. They are most commonly seen on external elevations, connecting a number of rainwater or above ground drainage runs together into a single soil stack.This 88 degree branch has a more swept design than the HS4034 branch, making it more suitable for foul rather than rainwater drainage. As Halifax pipes and fittings have no sockets, couplers are required to connect this branch to a pipe. A full dimensional drawing of this product can be found in the  Halifax technical catalogue.