Running a braided line for your cooling system. Billet Specialties new thermostat housings are now offered in -16 or -20 AN sizes for the small block/big block Chevy. Select from either a machined or black anodized finish. use with the stock thermostat or without a thermostat for racing. Precision machined fro.m 6061-T6 aluminum and includes stainless hardware and O-ring.