Stud Bolts vs. Through Bolts: Why Flange Joints Use Studs Instead of Ordinary Bolts
A stud bolt is a headless, double-ended fastener — one end is torqued permanently into a tapped hole and stays there, while the other end passes through the mating flange and takes a nut (often two nuts, "double-end studding," per ASTM A193 for common grades like B7). A through bolt is a conventional head-and-nut fastener that passes fully through both parts via clearance holes. Both clamp two parts together, but they solve that differently, and the difference matters most on flanged and pressure-retaining joints.
Why flange and pressure joints specify studs
Piping flanges (per ASME B16.5 and similar standards) and pressure vessel joints are frequently bolted with studs and two nuts rather than conventional bolts, for a few practical reasons: the stud stays permanently seated in the tapped hole, so maintenance work only removes the nut side without disturbing or wearing the base thread; even torque and preload distribution is easier to control on a symmetric double-nut arrangement; and studs allow "hot bolting" maintenance procedures on some in-service piping, where nuts can be worked on one at a time without fully de-tensioning the joint. Common stud material for elevated-temperature or pressure service is ASTM A193 Grade B7 alloy steel, paired with A194 Grade 2H nuts — always confirm the exact grade against your design code rather than assuming.
Where through bolts are the simpler choice
Through bolts remain the standard for general-purpose flange or plate connections that aren't governed by a piping/pressure code — lower-pressure equipment, structural connections, machine frames, and anywhere clearance holes on both mating parts are acceptable and there's no need to leave a permanent stud seated in a tapped hole. They're simpler to specify, stock, and install, since there's only one fastener type and length to manage instead of a stud-plus-two-nuts assembly.
Choosing between them
If your assembly is a piping flange, pressure vessel joint, or governed by a piping code, specify studs with the grade called out by that code. For general mechanical assembly without a pressure/piping code driving the joint, a through bolt is usually the simpler and more economical choice. Send your flange or joint drawing to our contact form and we'll confirm the correct configuration before sourcing through a partner factory.
Frequently Asked Questions
Can a through bolt be substituted for a stud bolt on a pressure flange?
Only if the governing code and flange rating permit it — many piping and pressure vessel standards specify stud bolts with matched nut grades for a reason, so substitution should be checked against the applicable code rather than decided on convenience alone.
What grade of stud material is typical for high-temperature service?
ASTM A193 Grade B7 alloy steel studs paired with A194 Grade 2H nuts are common for elevated-temperature and pressure piping applications, but the correct grade always depends on your specific design code and service conditions.