Hex Nuts
Hex Nuts Basics
Hex nuts are six-sided, hexagonal fasteners that are internally threaded and can be mated with externally threaded fasteners, such as a bolt, and by rotation, develop high clamping forces on structure contained between the nut and bolt bearing surfaces. A nut of a given thread size, material, heat treatment and adequate wall thickness has about 1.75 times the axial strength (tensile strength) of its mating bolt of the same material and heat treatment, provided that the effective thread length within the nut is equal to, or greater than, the major diameter of the bolt thread. This makes bolts the critical members in nut/bolt assemblies and makes nuts of the appropriate material and heat treatment ideal for bolt testing.
A finished hex nut, also known as a standard hex nut, has a smaller width across the flats and corners compared to a heavy hex nut. Heavy hex nuts are thicker and heavier in weight. The proof load strength is higher than a standard hex nut. Heavy hex nuts provide increased bearing surface area over finished nuts.
Hex Nuts Grades & Markings
Hex nuts are available in several different grades based on the mechanical and chemical properties of the material, and the intended application of the hex nut.
SAE J995 Grade 2 Hex Nuts
SAE J995 Grade 2 hex nuts are an economical, common low strength nut manufactured from low carbon steel. SAE J995 Grade 2 hex nuts are available in diameters from 1/4" through 1 1/2" inclusive. Grade 2 requires no material marking. These nuts are equivalent in strength to ASTM A563 Grade A nuts. Grade 2 nuts are commonly used in bolting applications with Grade 2 bolts, Grade 5 bolts, and A307 bolts.
SAE J995 Grade 5 Hex Nuts
SAE J995 Grade 5 hex nuts are medium strength nuts manufactured from quenched and tempered medium carbon steel. SAE J995 Grade 5 hex nuts are available in diameters from 1/4" through 1 1/2" inclusive. Grade markings include two circumferential lines located 120 degrees apart and the manufacturer's identification mark. Grade 5 hex nuts are commonly used on Grade 5 bolts.
SAE J995 Grade 8 Hex Nuts
SAE J995 Grade 8 hex nuts are high-strength nuts manufactured from quenched and tempered carbon alloy steel. Grade 8 hex nuts are available in diameters from 1/4" through 1 1/2" inclusive. Grade markings include two circumferential lines located 60 degrees apart and the manufacturer's identification mark. Grade 8 hex nuts are commonly used on Grade 8 bolts and A354 Grade BD bolts and are equivalent in strength to ASTM A563 Grade C nuts.
18-8 Stainless Steel Hex Nuts
18-8 stainless steel hex nuts are made from one of the following austenitic alloys: 303, 303Se, 304, XM7, all of which are characterized as having a chromium content of 17-19% and nickel content of 8-10%. There are no grade markings on 18-8 stainless hex nuts. 300 series stainless steel fasteners are commonly used in applications that require general atmospheric corrosion resistance, such as chemical and food processing equipment. Stainless steel has a higher corrosion resistance than carbon steel.
316 Stainless Steel Hex Nuts
316 stainless steel hex nuts are made from 316 stainless steel, an austenitic alloy which differs from 18-8 by its molybdenum content (2-3%) and a higher nickel content (10-14%). Nuts made of 316 stainless steel are marked "316". 316 stainless steel fasteners are commonly used in applications that require general atmospheric corrosion resistance, such as chemical and food processing equipment. More corrosion resistant than 18-8 stainless steel nuts.
Brass Hex Nuts
Brass Hex Nuts are manufactured from an alloy of copper and zinc. There are no grade markings on brass hex nuts. Brass fasteners are commonly used by electrical and communications industries, builders hardware and some marine applications. These nuts provide corrosion resistance in wet environments, offers thermal and electrical conductivity, and are nonmagnetic.
Silicon Bronze Hex Nuts
Silicon Bronze hex nuts are made from an alloy of mostly copper and tin, containing a small amount of silicon. There are no grade markings on bronze hex nuts. Fasteners made from silicon bronze are ideal for naval construction and are popular in the marine industry, because they are resistant to salt water, electrically conductive and nonmagnetic. They are also commonly used in general construction, refineries, and the power and energy industry as well. Compared to brass fasteners, bronze is much harder and more resistant to corrosion.
ASTM A563 Grade A Heavy Hex Nuts
ASTM A563 Grade A heavy hex nuts are made from carbon steel. Grade markings are not required for ASTM A563 Grade A heavy hex nuts, though in some cases Grade A nuts may be marked with the letter A. ASTM A563 covers standard specifications for carbon and alloy steel nuts.
ASTM A563 Grade DH Heavy Hex Nuts
ASTM A563 Grade DH heavy hex nuts are commonly used in structural bolting applications. ASTM A563 Grade DH covers standard specifications for carbon and alloy steel nuts. Grade markings consists of the grade symbol "DH". They are a common high strength nut used mainly in structural applications with F3125 Grades A325 and A490 bolting. In many applications, A194 Grade 2H nuts can be substituted for A563 Grade DH nuts.
ASTM A194 Grade 2H Heavy Hex Nuts
ASTM A194 Grade 2H heavy hex nuts are intended for use in flange bolting applications, as well as structural applications and with other high strength bolting. ASTM A194 Grade 2H covers carbon steel, alloy steel, and stainless steel nuts for bolts in high pressure or high temperature service. Grade markings consists of both the grade symbol "2H" and the manufacturer's identification mark. They are a common high strength nut used with many different bolting grades, including A193 Grade B7, F3125 Grades A325 and A490, as well as with F1554 Grade 105 anchor bolts and studs.
ASTM A194 Grade 2HM Heavy Hex Nuts
ASTM A194 Grade 2HM heavy hex nuts are quenched and tempered alloy steel nuts and are 100% hardness tested. ASTM A194 covers carbon steel, alloy steel, and stainless steel nuts for bolts in high pressure or high temperature service. Grade markings consists of both the grade symbol "2HM" and the manufacturer's identification mark. They are usually paired with A193 Grade B7M fasteners in applications where hydrogen sulfide gas exposure may lead to hydrogen embrittlement problems.
ASTM A194 Grade 8 Heavy Hex Nuts
ASTM A194 Grade 8 heavy hex nuts are manufactured from AISI 304 grade stainless steel and tested to meet ASTM A194 Grade 8. Grade markings for A194 Grade 8 heavy hex nuts consists of the number 8. Grade 8 stainless steel heavy hex nuts are intended for use in high-pressure and/or high-temperature service with ASTM A193 bolting of similar material, such as B8 and B8 Class 2.
ASTM A194 Grade 8M Heavy Hex Nuts
ASTM A194 Grade 8M heavy hex nuts are manufactured from AISI 316 grade stainless steel and tested to meet ASTM A194 Grade 8M. Grade markings for A194 Grade 8M heavy hex nuts consists of the number/letter combination of 8M. Grade 8M stainless steel heavy hex nuts are intended for use in high-pressure and/or high-temperature service with ASTM A193 and A320 bolting of similar material, such as B8M and B8M Class 2.
ASTM A194 Grade 7L Heavy Hex Nuts
ASTM A194 Grade 7L heavy hex nuts are manufactured from alloy steel, quenched and tempered. The ASTM A194 specification covers carbon steel, alloy steel, and stainless steel nuts for bolts in high pressure or high temperature service. They are a common high strength nut used with stud bolts for high and low temperature service, such as B16 and L7. When low temperature requirements are specified for Grade 7 nuts, the Charpy test procedures and requirements as defined in Specification A320/A320M for Grade L7 will apply. Grade markings consists of the grade symbol "7L".
Hex Nuts Finishes & Coating Materials
Hex nuts 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 Hex Nuts
Hex nuts are unfinished or will have a minimally protective finish. Black hex nuts offer near zero corrosion resistance, though black oxide coatings or oiled coatings do offer increased corrosion resistance over unfinished hex nuts.
- Black hex nuts are commonly referred to as plain finish, black, black oxide, black phosphate, bare or light oil coated.
Galvanized Hex Nuts
Hex nuts 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: Hex nuts 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 Hex Nuts
Hex nuts are coated with a thin layer of zinc, typically via electroplating.
- Plated hex nuts 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.
PTFE or Teflon Coated Hex Nuts
Hex nuts 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.