Methods and apparatus for coating substrates. A die can be employed for extrusion coating an elongated substrate, where the die defines a coating cavity therein. The die can comprise a die block having a coating supply channel for supplying a coating material to the coating cavity. The die can further comprise a guide plug and a die plate removably coupled to the die block. The guide plug can comprise a substrate inlet having a non-circular lateral cross-section, and the die plate can comprise a substrate outlet also having a non-circular lateral cross-section. A coating system comprising such a die can operate to coat a substrate where the substrate can be pushed at least partially through the die and contacts the coating material therein.