Stud Bolt Basics

All-thread stud bolts are fully threaded, have no head, are chamfered on each end and have a higher tensile strength compared to threaded bolts. They are most commonly used in conjunction with two nuts, typically heavy hex nuts. Stud bolts are well suited for a wide range of applications. By far, the most common application is flange bolting, though they are well suited and widely used for many other applications such as anchoring, automotive, and electrical. Industries utilizing stud bolts range from oil and gas, chemical and power, to the manufacturing, municipal, pipeline, and construction industries. All thread studs are available in a wide range of grades and materials.

 

Stud Bolt Grades & Markings

Stud bolts are available in several different grades based on the mechanical and chemical properties of the material, and the intended application of the stud bolt. Most stud bolts are identified by a material identification stamp on one end, along with the accompanying manufacturer’s mark on either the same end as the grade marking, or the opposite end. Some grades, such as F1554, can be identified by a color-coded marking on one end.

ASTM A193 vs ASTM A320

ASTM A193 covers the standard specifications for alloy steel and stainless steel bolting for high temperature or high pressure service. ASTM A320 covers standard specifications for alloy steel and stainless steel bolting for low temperature service. Typically, materials designed per ASTM A320 undergo additional testing above and beyond ASTM A193 to ensure materials will perform in low temperature applications.

A193 B7 Stud Bolts

ASTM A193 B7 stud bolts are by far the most common grade of stud bolt. High strength fasteners manufactured from a chromium-molybdenum steel and quenched and tempered. Grade markings consists of both the grade symbol "B7" and the manufacturer's identification mark on one end of each stud 3/8" diameter and larger. Inch series fasteners meeting ASTM A193 Grade B7 stud bolt specifications are extensively used in a wide range of flange bolting applications.

ASTM A193 Grade B16 Stud Bolts

High strength fasteners manufactured from heat treated Chromium-Molybdenum-Vanadium steel, quenched and tempered. Added Vanadium allows for operating temperatures higher than that of B7 stud bolts. Grade markings consists of both the grade symbol "B16" and the manufacturer's identification mark on one end of each stud 3/8" diameter and larger. Inch series fasteners meeting ASTM A193 Grade B16 stud bolt specifications are typically used in the power and petrochemical industries on boilers, turbines, and other pressurized equipment with elevated temperatures.

ASTM A320 Grade L7 Stud Bolts

Manufactured from AISI 4140/4142 alloy steel, quenched and tempered. Grade markings consists of both the grade symbol "L7" and the manufacturer's identification mark on one end of each stud 3/8" diameter and larger. ASTM A320 L7 stud bolts are intended for low temperature service. They have the same chemical and physical properties as ASTM A193 Grade B7, but must achieve a Charpy impact value of 20 lb-ft at -150F to ensure satisfactory performance in low temperature services. These fasteners are commonly used for valves, flanges, fittings, and pressure vessels in low temperature applications.

ASTM A193 B8 Stud Bolts

Manufactured from AISI 304 stainless steel and tested to meet ASTM A193. Grade markings consists of both the grade symbol "B8" and the manufacturer's identification mark on one end of each stud 3/8" diameter and larger. A193 grade B8 all thread studs are for use in pressure vessels, valves, flanges, and fittings for high temperature or high pressure service, or other special purpose applications.

A193 B8 Class 2 Stud Bolts

Manufactured from AISI 304 stainless steel, annealed and strain hardened to achieve increased strength characteristics per ASTM A193. Grade markings consists of both the grade symbol "B8SH" and the manufacturer's identification mark on one end of each stud 3/8" diameter and larger. A193 B8M Class 2 Stud Bolts are for use in pressure vessels, valves, flanges, and fittings for high temperature or high pressure service, or other special purpose applications where a high strength stainless steel is required.

A320 B8 Stud Bolts

Manufactured from AISI 304 stainless steel and tested to meet ASTM A320. Grade markings consists of both the grade symbol "B8" and the manufacturer's identification mark on one end of each stud 3/8" diameter and larger. For use in pressure vessels, valves, flanges, and fittings for low temperature service.

A320 B8 Class 2 Stud Bolts

Manufactured from AISI 304 stainless steel, annealed and strain hardened to achieve increased strength characteristics per ASTM A320. Grade markings consists of both the grade symbol "B8" and the manufacturer's identification mark on one end of each stud 3/8" diameter and larger. For use in pressure vessels, valves, flanges, and fittings for low temperature service. A193 grade B8 CL2 studs available designed for high temperature or high pressure service.

A193 B8M Stud Bolts

Manufactured from AISI 316 stainless steel and tested to meet ASTM A193. Grade markings consists of both the grade symbol "B8M" and the manufacturer's identification mark on one end of each stud 3/8" diameter and larger. For use in pressure vessels, valves, flanges, and fittings for high temperature or high pressure service, or other special purpose applications requiring higher corrosion resistance than 304 stainless steel.

ASTM A193 B8M Class 2 Stud Bolts

Manufactured from AISI 316 stainless steel, annealed and strain hardened to achieve increased strength characteristics per ASTM A193. Grade markings consists of both the grade symbol "B8MSH" and the manufacturer's identification mark on one end of each stud 3/8" diameter and larger. A193 B8M Class 2 all thread studs are for use in pressure vessels, valves, flanges, and fittings for high temperature or high pressure service, or other special purpose applications where corrosion resistant, high strength stainless steel is required.

A320 B8M Stud Bolts

Manufactured from AISI 316 stainless steel and tested to meet ASTM A320. Grade markings consists of both the grade symbol "B8M" and the manufacturer's identification mark on one end of each stud 3/8" diameter and larger. For use in pressure vessels, valves, flanges, and fittings for low temperature service, and where a stainless steel with higher corrosion resistance is needed.

A320 B8M Class 2 Stud Bolts

Manufactured from AISI 316 stainless steel, annealed and strain hardened to achieve increased strength characteristics per ASTM A320. Grade markings consists of both the grade symbol "B8M" and the manufacturer's identification mark on one end of each stud 3/8" diameter and larger. For use in pressure vessels, valves, flanges, and fittings for low temperature service where high corrosion resistance and high strength are needed.

A193 B8 Class 2B Stud Bolts

Manufactured from AISI 304 stainless steel, annealed and strain hardened to achieve increased strength characteristics per ASTM A193. Grade markings consists of both the grade symbol "B9" and the manufacturer's identification mark on one end of each stud 3/8" diameter and larger. ASTM A193 B8 Class 2B is a less common requirement commonly seen in the LNG industry. It has a higher minimum tensile strength than B8 Class 2 material in some cases. It also covers a larger range of material diameter. This spec does not have an ASTM A320 counterpart like many other grades of B8 and B8M stainless steel. Because of this, the A193 B8 Class 2B studs sold by STS are certified for use to -325° F, as they cannot be certified to ASTM A320.

 

Common Finishes of Stud Bolts

Stud bolts are available in a variety of finishes and coatings, which play a role in the suitability of the fasteners in different applications, such as enhancing resistance to corrosion from environmental elements or chemicals. Coatings also greatly effect consistency of torque values for installation, and ease of disassembly at the end of service.

Black or Plain Finish Stud Bolts

Stud bolts are unfinished or will have a minimally protective finish. Black stud bolts offer near zero corrosion resistance, though black oxide coatings or oiled coatings do offer increased corrosion resistance over an unfinished plain black stud bolt.

• Black stud bolts are commonly referred to as plain finish, black, black oxide, black phosphate, bare or light oil coated.

Galvanized Stud Bolts

Stud bolts are coated with a sacrificial zinc coating that acts as an anode to prevent the fastener underneath from corroding.

• Hot Dipped Galvanized: Fasteners are dipped in a bath of molten zinc.
• Mechanically Galvanized: Stud bolts are tumbled in a barrel with a mixture of water, zinc powder, other chemicals and glass beads. Although mechanical galvanizing results in a cleaner stud, it is an uncommon choice since it does not provide as much corrosion resistance as hot dipped galvanizing, due to the weaker bond between the steel and zinc.

Plated Stud Bolts

Stud bolts are coated with a thin layer of zinc or cadmium, typically via electroplating.

• Plated stud bolts will not corrode as quickly when covered with this protective coating, even when a scratch or cut exposes the steel to air or moisture. The zinc or cadmium plating will always tarnish and corrode first.

Teflon or PTFE Coated Stud Bolts

Stud bolts have a PTFE coating (commonly referred to as the Dupont tradename “Teflon”) and are formulated with superior characteristics for maximum fastener life.

• Technical components include a tensile strength of up to 4,000 psi and an operating pressure up to 100,000 psi. The absence of thread locking oxides enable easy and safe fastener removal. PTFE coatings have extreme chemical resistance and are ideal for applications including insulating piping, boiler rooms, water filled piping, water lines and more.