ASME B18.2.1 Bolts and Screws (2023)

ASME B18.2.1 is the standard specification covering the dimensional requirements for nine products types of inch series bolts and screws recognized as American National Standard. All dimensions of bolts and screws conforming to this standard are in inches and apply to unplated and uncoated product. When plating or coating is specified, the finished product dimensions shall be as agreed upon between supplier and purchaser. A bolt is an externally threaded fastener, generally used with a nut. It fits in an over-sized hole and is tightened by an end nut. A screw is also an externally threaded fastener, generally used without a nut. It normally fits in a threaded hole.

ASME B18.2.1 Nine Types of Bolts & Screws
Square Head BoltHex BoltHeavy Hex Bolt
Askew Head BoltHex Cap ScrewHeavy Hex Screw
Hex Flange ScrewLobed Head ScrewLag Screw

Construction and Manufacture

Bolts and screws manufactured in accordance with ASME B18.2.1 are all headed fasteners. The terminology “headed” indicates the basic construction style of the fastener, which is a partly or fully threaded rod or shank with a head. The head may be manufactured to various types such as square, hex, hex flange, and lobed, etc. Top of the head shall be full form and chamfered, with the diameter of chamfer circle equal to the maximum width across flats. The head height shall include the thickness of the washer face where provided. Besides, the head may be cross-drilled for self-locking purpose. Generally, the under-head surface and the washer face (if provided) are called bearing surface. As illustrated in Figure-1 and Figure-2, a fillet shall be furnished so that the head-to-shank transition can be more smooth which means low stress concentration.

ASME B18.2.1 Bolts and Screws (1)

Figure-1: a typical drawing of headed bolt conforming to ASME B18.2.1

(Video) ASTM A193 B8M HEX CAP BOLT ANSI B18.2.1

The body style furnished shall be either full size body or reduced body at the discretion of purchaser. The end of the shank shall be pointed (chamfered). The chamfer angle may vary depending on specific manufacturing process. The presence of the pointed end is to reduce the possibility of damage to the leading threads and to promote ease of assembly with a tapped hole or nut. The bolt or screw may be furnished in “full thread” (threaded for full length) or “half thread” (not threaded for full length, partly threaded) construction. The threads shall meet the requirements of ASME B1.1 except that lag screw thread dimensions are otherwise specified. Thread series on the bolts and screws may be coarse (UNC), fine (UNF), or 8 thread series (8 UN), except askew head bolts, which shall be unified coarse (UNC) only, and lag screws, which are otherwise specified.

(Video) ANSI/ASME B18.2.1 Hex Head Screws | Wenzhou Nanlong

ASME B18.2.1 Bolts and Screws (2)

Figure-2: a typical drawing of headed screw conforming to ASME B18.21.

(Video) ASME B18 Digital Fastener Catalog - 2 minute Demo

The first step in manufacturing of any bolt or screw is to cut the round bar to length. This process can be completed by either a shearing machine or a cutting saw. One end of the round bar is subsequently headed/ forged by an upsetter, in either hot forge or cold-worked conditions. Conventionally, round bars in diameter of 1″ and smaller shall be cold worked in the upsetter. When the diameter is larger than 1″, the round bar shall be preheated before forging by an induction coil to a specific temperature depending on material grade. The other end of the round bar shall be pointed (chamfered) prior to threading. The key process in manufacturing a bolt or screw is threading. Rolled threading and cut threading are the two major and different threading methods. Rolled threading is an extrusion process in which reduced body round bar is forced between two dies which displace the metal to form the threaded portion of the fastener, rather than cutting away the metal to form the thread. In cut threading process, the metal round bar is fed through a threader (threading machine) in which the metal is cut away from the round bar by thread chasers to form the threads.

Finish and Coating

According to ASME B18.2.1, the bolts and screws are routinely supplied with a plain (as processed) finish, unplated or uncoated. Upon client’s request, they can be furnished in various coatings such as light anti-rust oil coating, hot dipped galvanization, electrolytic zinc plating, cadmium plating, Xylan coating, PTFE coating (Teflon), zinc-aluminum coating, black oxide coating, and various powder coating, etc.


The ASME B18.2.1 bolts and screws may be manufactured from a comprehensive range of materials covering carbon steel, alloy steel, stainless steel, and nonferrous metal (Ti, Ni, Cu, Zr, etc). The typical standard specifications are listed in below table:

(Video) DIN931/DIN933/ASME B18 2 1 Hex bolt

Material Standards for ASME B18.2.1 Fasteners
ASTM A193Standard specification for alloy steel and stainless steel bolting materials for high temperature or high pressure service and other special purpose applications
ASTM A307Standard specification for carbon steel bolts and studs, 60000 psi tensile strength
ASTM A320Standard specification for alloy steel and stainless steel bolting for low-temperature service
ASTM A354Standard specification for quenched and tempered alloy steel bolts, studs, and other externally threaded fasteners
ASTM A449Standard specification for hex cap screws, bolts and studs, steel, heat treated, 120/105/90 ksi minimum tensile strength, general use
ASTM F468Standard specification for nonferrous bolts, hex cap screws, and studs for general use
ASTM F593Standard specification for stainless steel bolts, hex cap screws, and studs
MIL-F-18240Fastener element, self-locking, threaded fastener, 250°F Maximum
SAE J429Mechanical and material requirements for externally threaded fasteners

Conventionally: (1) All bolts except heavy hex bolts shall be furnished in ASTM A307 Grade A, or ASTM A354 Grade BC or BD; heavy hex bolts shall be conforming to ASTM A307 Grade B. (2) Hex head cap screws may be furnished in all grades of SAE J429 and ASTM A449, stainless steel of ASTM F593, nonferrous materials of ASTM F468. Heavy hex head cap screws may be furnished in all material grades in ASTM A193 and ASTM A320. Hex flange and lobed head screws are available in all carbon and alloy steel grades of SAE. (3) Lag screws are available in carbon steel ASTM A307 Grade A, stainless steel F593 Group 1, CW 304, and nonferrous materials of ASTM F468.

Important Dimensions

As illustrated in Figure-1 and Figure-2, there 5 important dimensions for each bolt or screw conforming to ASME B18.2,1. Thebolt or screw length, L: the distance measured parallel to the axis of fastener from the bearing surface of the head to the extreme end of the bolt or screw, including the point if the fastener is pointed. Thegrip gaging length, LG: the distance measured parallel to the axis of the bolt or screw from the under-head bearing surface to the face of the appropriate non-counterbored, non-countersunk special GO thread ring gage. Thebody length, LB: the distance measured parallel to the axis of the bolt or screw from the under-head bearing surface to the last scratch of thread or, for rolled threads, to the top of the extrusion angle. Thenominal thread length, LT: the length from the extreme point of the bolt or screw to the last complete thread. Thetransition thread length, Y: the length that includes the length of incomplete threads, the extrusion angle on rolled threads, and tolerances on grip length. Generally, the correlations between these dimensions are presented as: LG= L – LTand LB= LG– Y (both LTand Y are reference dimensions intended for calculation purposes only).

Inspection and Gaging

The bolts or screws shall be manufactured in accordance with respective material specifications. They not only shall meet all dimensional requirements specified by ASME B18.2.1 but also shall be conforming to the gaging requirements of ASME B1.1, ASME B1.2, ASME B1.3, and ASME B18.2.9. The tolerances shall be in accordance with ASME Y14.5.

(Video) Engineering: Is stud bolts covered under ASME B18.2.1


What is ASME B18 2.1 specifications? ›

Dimensions of ASME B18. 2.1 Hex Bolts
Nomianal Size or Basic product DiameterFull-Size Body Diameter, EHead Height, H
3/4 0.75000.7681/2
7/8 0.87500.89537/64
1 1.00001.02243/64
24 more rows

What is bolt ASME Code? ›

Which standard defines dimensions for bolts, nuts, and washers?
ASME B18.2.1Hex bolts, heavy hex bolts, square head bolts
ASME B18.2.2Hex nuts, heavy hex nuts, square nuts, hex jam nuts, heavy hex jam nuts, hex coupling nuts, lock nuts
ASME B18.2.6Structural bolts
ASME B18.21.1Standard flat washers, lock washers
1 more row
Dec 31, 2018

What is the standard for bolting? ›

The most common bolt ISO standards are:

ISO 898-1:2013 - This standard specifies the mechanical and material properties of bolts, screws and studs made of carbon steel and alloy steel used in bolting assemblies. It also specifies the methods for verifying these properties.

How much weight can a Grade 8 bolt hold? ›

Grade 8 bolts are designated as a 150 ksi. This means its tensile strength or the resistance it has before it is subject to breaking under tension is equal to 150,000 lbs.

What is the ASME standard for stud bolts? ›

Stud Bolt length are defined in ASME B16. 5 standard. The length in inches is equal to the effective thread length measured parallel to the axis, from the first to the first thread without the chamfers (points). First thread is defined as the intersection of the major diameter of the thread with the base of the point.

What is the difference between ANSI and ASME pipe? ›

ANSI accredits and established quality and performance standards for services and products in a huge variety of sectors, while the primary focus of ASME is on pressure vessels and boilers.

What ASME standard deals with screw threads? ›

1. This Standard specifies the thread form, series, class, allowance, tolerance, and designation for unified screw threads. (In order to emphasize that unified screw threads are based on inch modules, they may be denoted unified inch screw threads.)

How are bolts specified? ›

A bolt's size is classified based on a number of dimensions, namely the bolt's diameter, length of shank, thread pitch, grade, thread length and head size. Bolts can me specified in metric using millimeters, but the standard, internationally-recognized descriptions of bolt sizes are in inches.

What is the difference between SAE and ASTM bolts? ›

ASTM (American Society for Testing and Materials) covers primarily bolts and fasteners for construction applications. SAE (Society of Automotive Engineers) covers fasteners for automotive, machinery, and OEM applications.

What is the AISC bolt tolerance? ›

For anchor bolts to satisfy both AISC and ACI's tolerances, Suprenant and Malisch claim anchor bolts must be located within ± 1/16 inch of their specified location. A tolerance of ± 1/16 inch is neither realistic nor achievable.

What is the standard screw list? ›

U.S. standard numbering systems list diameter sizes 0, 1, 2 ,3, 4, 5, 6, 7, 8, 9, 10, 12, 14 and 16, and fractional sizes from 1/4" to 2" in 1/16" increments, followed by a dash and the threads per inch (from about 6 to 80), and the length.

How much weight can a 1 2 bolt handle? ›

Proof Load
Nom Bolt Size (in)Grade
12 more rows

What is the strongest bolt grade? ›

A grade 8 bolt is the highest grade SAE bolt. Grade 8 bolts have a minimum tensile strength of 150,000 PSI.

Is Grade 8 bolt harder than Grade 5? ›

Grade 8 / Grade G

Grade 8 bolts have been hardened more than grade 5 bolts. Thus they are stronger and are used in demanding applications such as automotive suspensions.

What is ASTM grade bolts? ›

ASTM A325 is an ASTM International standard for heavy hex structural bolts, titled Standard Specification for Structural Bolts, Steel, Heat Treated, 120/105 ksi Minimum Tensile Strength. It defines mechanical properties for bolts that range from 1⁄2 to 11⁄2 inches (13 to 38 mm) in diameter.

What is the difference between ANSI B16 5 and ASME B16 47? ›

However, the standard ASME B16 5 (ANSI B16 5) only covers size up to 24 inches. For bigger sizes, ASME B16. 47 standard covers pressure-temperature ratings, materials, dimensions, tolerances, marking, and testing for pipe flanges in sizes NPS 26 through NPS 60 and in ratings Classes 75, 150, 300, 400, 600, and 900.

What is the yield strength of ASME bolts? ›

ASME Specification SA– 453 / SA-453M

Their yield strength ranges from 50 to 120 ksi (345 to 827 MPa). The material is for use in high-temperature service such as fasteners for pressure vessel and valve flanges.

Are ASME and ASTM the same? ›

ASTM is responsible for the development and re-enactment of standards for all types of old and new materials. Because it is the test and materials association. ASME is to selectively absorb and filter these standards for the relevant works used, and to be modified to improve.

How do ASTM and ASME compare? ›

Basically ASTM creates the material specifications and standard test methods to determine compliance. ASME selects those ASTM materials which will perform adequately in boiler or pressure vessel service and accepts them with stated limitations.

How many types of ASME are there? ›

ASME has two institutes and 32 technical divisions within its organizational structure.

What is ASME B18? ›

ASME B18. 2.1 is the standard specification covering the dimensional requirements for nine products types of inch series bolts and screws recognized as American National Standard. All dimensions of bolts and screws conforming to this standard are in inches and apply to unplated and uncoated product.

What are the 4 types of screw threads? ›

There are Standard threads, ACME threads, Buttress threads, and Square threads. Each of these threads may be used in clamps and vises for different reasons.

What are the standards for screw threads? ›

For Unified inch screw threads there are six standard classes of fit: 1B, 2B, and 3B for internal threads; and 1A, 2A, and 3A for external threads. All are considered clearance fits. That is, they assemble without interference. The higher the class number, the tighter the fit.

What are the three basic types of bolts? ›

The principal types of bolts commonly used include: Anchor Bolts. Blind Bolts. Carriage Bolts.

How do I choose a bolt grade? ›

This is how you choose the right bolt for the joint:
  1. First, identify the load case.
  2. Determine the necessary clamping force in the joint.
  3. Choose the smallest bolt diameter that can support the clamp load.
  4. Choose an effective bolt securing method.
  5. Decide on the most appropriate tightening method.

What is ASTM specification for steel bolts? ›

ASTM steel bolts - proof and tensile strength.
ASTM DesignationSize Range (in)Minimum Tensile Strength (103 psi)
A325 type 31/2 - 1 1 1/8 - 1 1/2120 105
A354 grade BC
A354 grade BD1/4 - 4150
A4491/4 - 1 1 1/8 - 1 1/2 1 3/4 - 3120 105 90
5 more rows

Which bolts are better ASTM A325 or A 490? ›

A490 bolts are more susceptible to brittle fracture than A325 bolts which are 120/105 minimum tensile strength steel. To minimize the risk of brittle fracture A490 bolts have both a minimum and a maximum tensile strength specified. FHWA recommends that A325 bolts be used wherever possible.

What is the formula for bolts? ›

The tensile load a fastener can withstand is determined by the formula P = St x As. To find the tensile strength of a particular bolt, you will need to refer to Mechanical Properties of Externally Threaded Fasteners chart in the Fastenal Technical Reference Guide.

What is the bolt tightening formula? ›

The widely recognized engineering formula, T= K x D x P (to be explained later in this article), was used to provide the chart's values, but it must be understood that every bolted joint is unique and the optimum tightening torque should be determined for each application by careful experimentation.

What is allowable bolt stress? ›

The maximum allowable stress in the bolt due to pressure, thermal and external loading is defined to be 0.83 times the minimum yield strength based on the nominal stress in the bolt at the minimum root diameter.

What is typical screw tolerance? ›

As an example, a common screw thread tolerance is 5g6g, which indicates a 5g tolerance on its pitch diameter, and a 6g tolerance on its external (thread) diameter. Screw threads with identical external tolerances and pitch tolerances are expressed with a single tolerance letter and number.

What is the maximum bolt spacing as per AISC? ›

According to the AREMA commentary, these requirements were adopted in 1943 and were based on experience and judgment. The AISC Specification requires a maximum bolt spacing of 24t ≤ 12 in.

What do the 2 numbers on screws mean? ›

The first number is the diameter. The bigger the number the bigger the screw. The second number is the number of threads per inch. Check your state and local codes before starting any project. Follow all safety precautions.

What does the M mean in screw size? ›

The letter 'M' indicates that this bolt uses a metric thread. The number '8' refers to the nominal diameter of the bolt shaft in millimeters. The number 1.0 is the thread pitch of the bolt, which is the distance between threads, in millimeters. And the final figure, 20, is the length in millimeters.

What does the G mean on screws? ›

Self Tapping Screw Gauge (g) Size (mm)

What should a 1 2 bolt be torqued to? ›

US Recommended Bolt Torque
SizeRecommended Torque
Grade 2Grade 8
13 more rows

What is the minimum distance between two bolts? ›

Explanation: Distance between centres of any two consecutive fasteners in line adjacent and parallel to edge of outside plate shall not exceed (100+4t) or 200mm, whichever is less in compression and tension members.

How much load can a 1 2 lag bolt hold? ›

Hex Galvanized Lag Screw is 1/2 in. Helpful? Q:What is the maximum shear load of each bolt? A: It will depend on the type of wood being used and application, but it is rated for shear strength of 430 lbs.

What is the hardest bolt to break? ›

Grade 8 is the hardest, Grade 5 is medium, and Grade 2 is the softest. This is the most common grade of steel fastener and is the least expensive. Grade 2 bolts have no head marking, although sometimes a manufacturer's mark is present. This grade of bolt is made from low or medium carbon steel.

Is stainless steel stronger than steel? ›

Chemical composition

Steel generally has a lower carbon content than stainless steel, making it slightly stiffer and stronger. Stainless steel production follows the same steps as steel production, but takes it a step further by adding chromium, nickel, nitrogen, and molybdenum.

What do letters on bolts mean? ›

You can usually figure out the grade, or strength, of a bolt by looking at the markings on its head. English bolts (U.S.S. or S.A.E) are categorized by grade, from grade 2 to grade 8, where the grade represents inch strength. The higher the grade, the stronger the bolt.

How much force does it take to break a Grade 8 bolt? ›

Grade 8 bolts are designated as a 150 ksi. This means its tensile strength or the resistance it has before it is subject to breaking under tension is equal to 150,000 lbs.

What screw material is strongest? ›

Titanium. The most durable material for screws and fasteners is titanium. Titanium fasteners are common within the aerospace industry and other heavy-duty applications. Titanium fasteners are also used in medical applications like bone screws.

Is there a Grade 10 bolt? ›

Class 10. This is a metric nut grading similar to the SAE grade 8 classification, which is used in conjunction with Class 10.9 bolts. This strength of nut is used in automotive, and structural industries, as well as in high temp applications.

What does ASME B18 6.3 mean? ›

ASME B18. 6.3 : Machine Screws, Tapping Screws, and Metallic Drive Screws (Inch Series) by Accuris. Item. Format.

What is ASME B18 13? ›

13 Machine Screw and Washer Assemblies - Sems by Material, Finish and Size. SEMS® Machine Screws are machine screws with pre-assembled captive washers, designed to speed total assembly time in a manufacturing process. Search thousands of US/Imperial fasteners by ANSI specification, including ANSI/ASME b18.

What is the astm standard specification for structural bolts steel heat treated 120 105 ksi minimum tensile strength? ›

ASTM A325 is an ASTM International standard for heavy hex structural bolts, titled Standard Specification for Structural Bolts, Steel, Heat Treated, 120/105 ksi Minimum Tensile Strength. It defines mechanical properties for bolts that range from 1⁄2 to 11⁄2 inches (13 to 38 mm) in diameter.

What is ASTM A193 gr B7? ›

ASTM A193 Grade B7 is a standard specification for high tensile alloy steel bolting material for use in high temperature or high-pressure service and other special purpose applications. It covers material specification for bolting used in pressure vessel service, valves, flanges and fittings.

What is ASME B18 2.1 bolt grade? ›

ASME B18. 2.1 is the standard specification covering the dimensional requirements for nine products types of inch series bolts and screws recognized as American National Standard. All dimensions of bolts and screws conforming to this standard are in inches and apply to unplated and uncoated product.

Is there a difference between ANSI and ASME flanges? ›

ASME Flanges are based on guidelines and regulations for mechanical devices, while ANSI Flanges are based on standards developed by associations. ANSI flanges are generated using approximately 9500 standards, whereas ASME flanges are produced using 600 codes and regulations for various mechanical devices.

What class is a machine screw? ›

Unlike Machine Bolts, which are large and can range up to M48 and larger, Machine Screws are usually M10 and smaller although a few M12 and M16 are available. Even though some are Class 8.8, most are Class 4.8 which renders them appropriate for light-duty applications only.

What does ASME mean on a flange? ›

ASME is the abbreviation for the American Society of Mechanical Engineers a group of mechanical engineers and representatives from engineering companies–also non-profit–establishing standards and codes for mechanical devices such as boiler components and fasteners as well as actively promoting these standards through ...

What ASTM is most structural steel? ›

ASTM A992 (A572 Grade 50) steel is the most used construction-based structural steel in existence. It is used to make I beams, Wide Flange, channels, plates, angles, and other shapes.

What is the ASTM standard for high strength bolts? ›

A grade 8 bolt is the highest grade SAE bolt. Grade 8 bolts have a minimum tensile strength of 150,000 PSI. As a comparison, the ASTM A325 bolt is roughly equivalent to the SAE grade 5. A grade 8 bolt would be one that meets ASTM A490 standards.

What is ASTM for tensile test for bolts? ›

ASTM F606 is a test method that establishes testing procedures for determining the mechanical properties of externally and internally threaded fasteners, washers, direct tension indicators, and rivets. Bolt and fastener testing is very common in the automotive and industrial/consumer products industries.

Is B7 stronger than Grade 8? ›

With a minimum tensile strength of 150 ksi and a minimum yield of 130 ksi, Grade 8 has a higher tensile and yield strength than other steel grades such as Grade 5 and B7. It is also quenched and tempered at 800 F leading to its strength.

What is the difference between B7 and B16 bolts? ›

The “big brother” of B7 studs, B16 studs are found in similar situations, but are specified when a higher temperature is required. Vanadium is the main composition difference that separates B16 from B7, allowing the higher temperature limits.

What is the difference between B7 and B7M bolts? ›

ASTM A193 Grade B7M bolts and studs are identical in chemistry to Grade B7 (quenched and tempered medium carbon alloy steel), but have lower strength requirements and require 100% hardness testing of all fasteners manufactured in the lot.


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