Threaded Rods & Studs are the preferred products for fastening pipe flanges, as well as many other applications.
Studs are available fully threaded, double & single end thread. Fully threaded Studs are usually used when flange bolting with two Nuts applied.
ASTM A193, A320, A354, A453, Carbon Steel, Stainless & non Ferrous grades B5, B6, B7, B7M, B8… Duplex 2205™, Hastelloy C276™ …..(see entire list here)