ASME B18.31.2 Continuous Thread Studs

ASME B18.31.2 continuous thread studs are inch-series fasteners with thread running from end to end. There is no unthreaded shank and no reduced-diameter section. The full thread profile is continuous, so a nut can be positioned anywhere along the stud body. This is the defining physical characteristic of the product and the reason it is selected for flanged joints where nut location must be adjusted to suit the assembly.

In a flanged connection, the stud passes through aligned bolt holes in two flanges, a gasket, and sometimes a spacer or blind. The nut position is not fixed by a shank; it is set by where the nut is run down on the thread. A continuous thread stud therefore accommodates variations in flange thickness, gasket compression, and stack-up without requiring a different stud length for each combination. One stud length can serve multiple flange assemblies within its range. The thread also extends into the unclamped portion of the stud, so any exposed length beyond the nut remains threaded rather than showing a plain shank.

The ends of ASME B18.31.2 continuous thread studs are chamfered as standard, with rounded or 45° bevel ends available where installation conditions require them. Threads are unified inch series — UNC, UNF, or 8UN — with the 8-thread series used for diameters 1 inch and above. Nominal diameters run from 1/4 inch through 4 inches, and lengths are specified from 1 inch up to 48 inches depending on diameter. The product is commonly supplied in inch-series dimensions only; metric equivalents are covered by separate standards. In catalogues and purchase orders, these items also appear as all-thread studs, fully threaded stud bolts, or flange studs.

The typical installation is a raised-face or ring-joint flange in a piping system, where the stud is inserted through the bolt holes and two nuts are run down, one on each side, to compress the gasket. Continuous thread studs are used in refinery, petrochemical, and power piping where flanged joints are assembled and disassembled during maintenance. The selection consideration is the thread series and diameter required by the flange bolt hole, and the stud length needed to cover the flange thickness plus nut height plus any washer or spacer.