Profile: C.A. Schroeder, Inc. manufactures spiral pipe, molded round duct liner, flexible aluminum duct, hinged face diffuser and collars. Our spiral pipe is manufactured from commercial grade G90/G60 galvanized coating. These pipes are available in diameters from 4" through 66". These pipes are ideally suited for all types of air distribution systems. Our Circliner is a molded round fiberglass duct liner for heating and air conditioning systems.