Stud bolt, nuts, machine bolts, and washers are also known as bolting material or fastener. Bolting is the term that used to tighten/create the flange joints connection. The tightening of the flange ensures the leak-proof connection between gasket & flanges.
ASME flanges have a minimum four bolt hole and for higher diameter flanges, the number of bolt holes is always in multiples of four. Selection of number bolt holes depends on the factor such as
Size of the flange
Different Kinds of Fasteners Used in Piping
The stud has a thread on full-lengths or at both ends. As shown in images. It is having three components if washers are not used (two nuts and stud). If you used washer it would become five. Sometimes additional nuts are used for hydraulic tensioning with larger size stud.
The length of the stud bolt should be enough to cover the entire Nut plus 1.5 to 3 threads exposed. Long studs must be avoided as it increases the chance of corrosion and other damage to exposed threads, which would make subsequent removal difficult.
ASME B16.5 gives the required size of the stud. The length of the stud depends on the type of gasket and the maximum exposed thread requirements.
Bolts have a thread at one end and hexagonal head on another end. See the image below. In the process, piping bolts are used with lower strength flange types such as GRE/GRP, bronze. Usually, washers are used with a bolt to prevent excessive load to the flange.