3/8" UNF x 24 TPI Female Brass Brake Pipe Fittings. Thread size is3/8" x 24 TPI UNF, specifically designed for3/16" pipe size. 3/8" x 24 TPI UNF. High-quality female brake pipe fittings manufactured from durable solid brass, designed for use with 3/16" copper or copper-nickel brake pipes.