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While heavy nut is a broader term used to describe a heavy pattern nut, we will focus on ASTM A194 nuts used with stud bolts.  

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Inventory

MSI Supply stocks a full range of nuts to support our stud bolt inventory, which for carbon steel means 1/2” - 2” diameter in: Plain (black) finish, Teflon Blue, and Cad Plating.  MSI also stocks stainless heavy nuts from ¼ - 1-1/2”.  MSI can also provide larger heavy nuts, heavy nuts made from special alloys, and many different coatings. However, some of these items may be subject to a lead time.

Size Range: 1/4" to 4" Diameter (Metric & Standard)
Types: Acorn, Coupling, Hex, Flange, Heavy Hex, Jam, Lock
Carbon Steel: Grade 2, Grade 5, Grade 8, 2H, 2HM
Stainless Steel: 18-8, 304 SS, 316 SS, Grade 8, Grade 8M
Exotic Alloys: A20, 17-4PH, MonelInconelIncoloyHastelloy, Brass, Titanium, Silicon Bronze
Coatings: Black Oxide, Cadmium, Galvanized, Teflon, Xylan, Zinc, Others Upon Request

 

Thread Pitch

Thread pitch refers to the steepness of the angle of thread, which is measured in threads per inch.  MSI’s Thread Pitch Chart (link to chart) shows the unified screwed thread for coarse and fine thread, as well as the thread pitch for stud bolts. Heavy nuts covered under the A194 utilize 8UN for all diameters 1” and above, meaning there are 8 threads per inch for these sizes. 

Material

Stud bolts can be made from many different grades of material, but the most common materials are listed below.  The link to the A194 page provides the chemical and mechanical properties of these materials. 

Carbon Steel

2:        Carbon Steel heavy hex

2H:     Quenched and Tempered carbon steel heavy hex nut

2HM: Quenched and Tempered carbon steel heavy hex nut w/100% hardness tested

4:        Quenched and Tempered carbon-molybdenum heavy hex nut

Alloy Steel

7:        Quenched and Tempered alloy steel heavy hex nut

7M:    Quenched and Tempered alloy steel heavy hex nut w/100% hardness tested

7L:      Quenched and Tempered alloy steel heavy hex nut w/Charpy impact test

Stainless Steel

8:        Stainless steel (304) heavy hex nuts, can be class 1 or 2 and can be in annealed condition (A194-8A)

8M:    Stainless steel (316) heavy hex nuts, can be class 1 or 2 and can be in annealed condition (a194-8MA)

A194 Specification

A194 is the ASTM specification covering carbon, alloy, and stainless steel hex nuts intended for use in high pressure and/or high-temperature service applications.  Unless specified, the Heavy Hex series (B18.2.2) shall be used.  Hex nuts up to 1" in diameter should be UNC, anything after will be 8UN.

Class 1 vs Class 2

Class 1 products are made from solution-treated material. Class 2 products are made from solution-treated material that has been strain hardened. Austenitic steels in the strain hardened condition may not show uniform properties throughout the cross section, particularly in sizes over 3/4" diameter.  For instance, A193 B8 and B8M are standardly provided as class 1 but are also available in class 2.

Related Hardware

This chart shows the nuts that accompany the stud bolts and washers, by grade.  These items are required for proper installation.

Stud Bolt Grade

Nuts

Washers

L7

A194 Grade 4 or 7

F436

L43

A194 Grade 4 or 7

F436

B8 Class 1

A194 Grade 8

SS304

B8M Class 1

A194 Grade 8M

SS316

B8 Class 2

A194 Grade 8

SS304

B8M Class 2

A194 Grade 8M

SS316

B7

A194 Grade 2H

F436

B7M

A194 Grade 2HM

F436

B16

A194 Grade 4 or Grade 7

F436

 

Grade Identification Markings

Grade Identification

 

Coating and Plating

Nuts are most commonly available with a plain finish, which is also referred to as Black.  However, there are also numerous applications that call for coating/plating, with the most common Teflon Blue coating.  Teflon, or Xylan, coating provides for increased corrosive resistance, which is favorable that require increased corrosion resistance as well as the strength of carbon steel.