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Studbolts & Hex Nuts

Studbolts & Hex Nuts

  • ASTM A193
  • ASTM A320
  • ASTM A453
  • ASTM A182
  • ASTM A194 (Nuts)
  • ASTM F467 (Nuts)


Studbolts are available in many diameters and lengths, metric, and imperial, in a variety of materials from Carbon and Low Alloy to Stainless and the Nickel Alloys.

The material of the hex steel nuts shall match the material of the threaded rod (generally, stud materials ASTM A193 match with nuts materials ASTM A194).

The ASME B16.5 specification covers Studbolts and nuts for ASME flanges (number, the diameter and the length of required stud bolts, i.e. “flange bolt chart”) by flange diameter, pressure class and face finish (RF, FF, RTJ).

Studbolts Materials

The most common materials for stud bolts (for flanges) are ASTM A193 (grade B7, B8, B8M, B8T), ASTM A453 (grade 660), ASTM A320 (grade L7, L7M), and ASTM A182 (duplex and super duplex bolting). For aggressive environments and fluids, stud bolts can be coated (see below ‘Coated Studbolts’)

ASTM A193 Studbolts (High-Temp)

The ASTM A193 specification covers alloy-steel and stainless steel stud bolts materials for high temperature or high-pressure service.

The most common stud bolts materials covered by ASTM A193 are:

  • ASTM A193 B5
  • ASTM A193 B6
  • ASTM A193 B7: Alloy steel, AISI 4140/4142 quenched and tempered
  • ASTM A193 B7M
  • ASTM A193 B16
  • ASTM A193 B8: Class 1 Stainless steel, AISI 304, carbide solution treated.
  • ASTM A193 B8A
  • ASTM A193 B8M: Class 1 Stainless steel, AISI 316, carbide solution treated.
  • ASTM A193 B8MA
  • ASTM A193 B8T (SS 321)
  • ASTM A193 B8cl2: Class 2 Stainless steel, AISI 304, carbide solution treated, strain hardened
  • ASTM A193 B8Tcl2

Coated Studbolts

Stud bolts can be coated to increase the resistance to corrosion. The most common types of coatings for stud bolts are listed below:

  •   Electro zinc plating
  •   Electro cadmium plating
  •   Hot dip galvanizing
  •   PTFE Coating
  •   Phosphate coating
  •   Electroless nickel plating
  •   Zinc-nickel coating
  •   Aluminium coating
  •   Silver coating
  •   XYLAN 1070
  •   XYLAN 1024

 Threading for Studbolts

The Stud Bolt is threaded according to the specifications set by ASME B1.1.

  • UNC is the most common type for Stud Bolts and Nuts. Including A193 B7, A193 B8/B8M and A320 for sizes 3/8” to ¾” Coarse threads are used for threads in low strength materials such as iron, mild steel, and softer alloy. The coarse thread is also more tolerant of adverse conditions
  • Fine thread series (UNF/UNRF): UNF is widely used for precision duties and when higher tensile strength is required
  • 8-Thread series (8UN) is the threading method for several ASTM standards including A193 B7, A193 B8/B8M, and A320. This series is widely used for diameters from one inch upwards. There are 8 threads per inch for these sizes.
  • For any other material grade, the customer shall specify the thread pitch unless it is given by the applicable ASTM norm.

Hex Nuts for Studbolts

The mechanical strength of the steel nut material shall be compatible with the strength of the mated Stud Bolts.

Hex Nuts (dimensions and weights) are defined in ASME B18.2.2.as bolts the threading in ASME B1.1. Depending on customer specification, nuts must be both sites chamfered or with on one side a washer-face.

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