Stud bolts and nuts are always work together. If the stud bolt grade is ASTM A193, the nut grade should also match the right ASTM A194 grade. For flange connection, pressure piping, valves, and oil & gas projects, this small detail is very important.
ASTM A193 is the standard for alloy steel and stainless steel stud bolts used in high-pressure and high-temperature service. ASTM A194 is the standard for matching heavy hex nuts. In common use, ASTM A193 B7 stud bolts match ASTM A194 2H nuts, B7M matches 2HM, B8 matches Grade 8, and B8M matches Grade 8M. Buyers should check grade marking, MTC, heat number, coating, and thread fit before shipment.
In this article, I will not repeat too much about every bolt grade. We already talk about ASTM A193 B7 vs B7M stud bolts in other guides. Here, we only focus on one thing: how to match ASTM A193 stud bolts with ASTM A194 nuts.
Why Stud Bolts Need the Right ASTM A194 Nuts？
A stud bolt is usually used with two nuts. In flange connection, the stud bolt goes through the flange holes, and nuts are tightened on both sides. The bolt and nut share the load together.
So the nut is not only an accessory. It is part of the bolting set. If the stud bolt is B7, the nut should also meet the proper strength and standard requirement. If the stud bolt is B7M, the nut grade also need to follow the project requirement.
ASTM A193 vs ASTM A194: What Each Standard Controls
ASTM A193 controls the bolting material. It covers alloy steel and stainless steel bolting for high-pressure, high-temperature, and special purpose service. Common A193 grades include B7, B7M, B16, B8, B8M, B8C, and B8T.
ASTM A194 controls the nut material. It covers carbon steel, alloy steel, martensitic stainless steel, and austenitic stainless steel nuts for high-pressure or high-temperature service. For A193 stud bolts, the nuts are normally heavy hex nuts.
The simple rule is this: ASTM A193 tells you what the stud bolt is. ASTM A194 tells you what the nut is. When buying a complete bolting set, both standards should appear clearly in the order.
ASTM A193 Stud Bolt Grade and ASTM A194 Nut Matching Table
The table below is a common matching guide for ASTM A193 stud bolts and ASTM A194 nuts. It is useful for quotation and order checking. For final order, please follow the drawing and project specification.
| ASTM A193 Stud Bolt Grade | Common ASTM A194 Nut Grade | Simple Note |
|---|---|---|
| ASTM A193 B7 | ASTM A194 2H; Grade 7 if specified | Common alloy steel stud bolt set |
| ASTM A193 B7M | ASTM A194 2HM | Lower hardness bolting set, often used for sour service |
| ASTM A193 B16 | ASTM A194 7 or 16, according to project | Used for higher temperature service |
| ASTM A193 B8 Class 1 / Class 2 | ASTM A194 Grade 8 | 304 stainless steel bolting set |
| ASTM A193 B8M Class 1 / Class 2 | ASTM A194 Grade 8M | 316 stainless steel bolting set |
| ASTM A193 B8C | ASTM A194 Grade 8C | 347 stainless steel bolting set |
| ASTM A193 B8T | ASTM A194 Grade 8T | 321 stainless steel bolting set |
Some matching charts may show more options for a grade. But in real order, the project drawing is always the first rule. If the drawing says 2H, use 2H. If it says 2HM, use 2HM. We should not change nut grade only because another grade is easier to find.
Heavy Hex Nuts Are Usually Used with A193 Stud Bolts
For ASTM A193 stud bolts, heavy hex nuts are usually used. Heavy hex nuts have larger width across flats than regular hex nuts. They are more suitable for flange bolting and pressure equipment.
Regular hex nuts may look close in a photo, but they are not the same. The width, thickness, and wrench size can be different.
If the drawing gives nut dimension, we follow the drawing. If the drawing only says ASTM A194 nuts, we will confirm the nut type with customer before production.
Coating and Thread Fit
Surface treatment can affect thread fit. It is a small detail, but very practical.
Hot dip galvanizing adds coating thickness. The nuts may need proper overtapping. PTFE coating can change friction during tightening. Zinc plating, Geomet, Magni, Zn-Ni, black finish, and plain finish also have different effects on assembly.
When we supply coated stud bolts and nuts, we can test the nut running condition before packing. It is better to check thread fit before shipment than after the goods arrive.
Do Stud Bolt and Nut Sets Need Washers?
Stud bolt sets do not always need washers. Many flange connections use stud bolts and heavy hex nuts directly.
Some projects may require washers to protect the surface or meet installation rules. In this case, the washer standard, material, hardness, coating, and quantity should be written clearly.
Do not add washers only by habit. Washers can affect thread engagement and total grip length. The best way is to follow the drawing or ask the project engineer.
Contact Hengrui Fastener for Custom Stud Bolt and Nut Set
Shanghai Hengrui Industrial Co., Ltd supplies standard and non-standard fasteners, custom machining parts, and stamping parts for B2B, OEM, and wholesale buyers. If you are not sure which ASTM A194 nut should match your ASTM A193 stud bolt, contact us your drawing, project specification, coating requirement, and inspection rule. We will help you check before production. A nut is small, but it has a big vote in whether your bolting set passes inspection.
