Bolt Hole Diameter for Flanges (Charts & Guide)

Bolt hole diameter for flanges plays an important role in the assurance of two of the major concerns: performance and safety of these essential components. They are primarily used to connect pipes, valves, and other equipment in different industries. The bolt holes on the flanges enable leak-free assembly with structural damages prevented.

Among the most important things in tight and reliable connection is selection and determination of the bolt hole diameter. The properly designed diameter of a bolt hole helps in optimum distribution of forces and load-carrying capacity to prevent failure.

As one of the largest manufacturers of flanges, YANHAO understands that bolt hole diameter significantly affects the general performance and safety of flange systems. From experience and determination, we understand that any calculation and design of bolt hole diameters in every process should deliver superior-quality flanges beyond the expectation of our customers and the highest set standards within the industry.

If you are an expert in this industry and just want to know the common flange and the corresponding bolt hole parameters, then just look at the table below.
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ASME/ANSI B16.5 Flanges and Bolt Dimensions

Note: 1 inch = 25.4 mm

Nominal Pipe Size (NPS)
(inches)		Diameter of
Flange
(inches)		No.
of
Bolts		Diameter of
Bolts
(inches)		Diameter of
Bolt Holes
(inches)		Bolt
Circle
(inches)
1/43-3/841/20.622-1/4
1/23-1/241/20.622-3/8
3/43-7/841/20.622-3/4
14-1/441/20.623-1/8
1-1/44-5/841/20.623-1/2
1-1/2541/20.623-7/8
2645/80.754-3/4
2-1/2745/80.755-1/2
37-1/245/80.756
3-1/28-1/285/80.757
4985/80.757-1/2
51083/40.888-1/2
61183/40.889-1/2
813-1/283/40.8811-3/4
1016127/8114-1/4
1219127/8117
14211211.1218-3/4
1623-1/21611.1221-1/4
1825161-1/81.2522-3/4
2027-1/2201-1/81.2525
2432201-1/41.3829-1/2
https://carbonsteelflanges.com/ansi-b16-5-class-150-flanges
Nominal Pipe Size (NPS)
(inches)		Diameter of
Flange
(inches)		No.
of
Bolts		Diameter of
Bolts
(inches)		Diameter of
Bolt Holes
(inches)		Bolt
Circle
(inches)
1/43-3/841/20.622-1/4
1/23-3/441/20.622-5/8
3/44-5/845/80.753-1/4
14-7/845/80.753-1/2
1-1/45-1/445/80.753-7/8
1-1/26-1/843/40.884-1/2
26-1/285/80.755
2-1/27-1/283/40.885-7/8
38-1/483/40.886-5/8
3-1/2983/40.887-1/4
41083/40.887-7/8
51183/40.889-1/4
612-1/2123/40.8810-5/8
815127/8113
1017-1/21611.1215-1/4
1220-1/2161-1/81.2517-3/4
1423201-1/81.2520-1/4
1625-1/2201-1/41.3822-1/2
1828241-1/41.3824-3/4
2030-1/2241-1/41.3827
2436241-1/21.6232
https://carbonsteelflanges.com/ansi-b16-5-class-300-flanges
Nominal Pipe Size (NPS)
(inches)		Diameter of
Flange
(inches)		No.
of
Bolts		Diameter of
Bolts
(inches)		Diameter of
Bolt Holes
(inches)		Bolt
Circle
(inches)
1/43-3/841/20.622-1/4
1/23-3/441/20.622-5/8
3/44-5/845/80.753-1/4
14-7/845/80.753-1/2
1-1/45-1/445/80.753-7/8
1-1/26-1/843/40.884-1/2
26-1/285/80.755
2-1/27-1/283/40.885-7/8
38-1/483/40.886-5/8
3-1/2987/817-1/4
41087/817-7/8
51187/819-1/4
612-1/2127/8110-5/8
8151211.1213
1017-1/2161-1/81.2515-1/4
1220-1/2161-1/41.3817-3/4
1423201-1/41.3820-1/4
1625-1/2201-3/81.522-1/2
1828241-3/81.524-3/4
2030-1/2241-1/21.6227
2436241-3/41.8832
https://carbonsteelflanges.com/ansi-b16-5-class-400-flanges
Nominal Pipe Size (NPS)
(inches)		Diameter of
Flange
(inches)		No.
of
Bolts		Diameter of
Bolts
(inches)		Diameter of
Bolt Holes
(inches)		Bolt
Circle
(inches)
1/43-3/841/20.622-1/4
1/23-3/441/20.622-5/8
3/44-5/845/80.753-1/4
14-7/845/80.753-1/2
1-1/45-1/445/80.753-7/8
1-1/26-1/843/40.884-1/2
26-1/285/80.755
2-1/27-1/283/40.885-7/8
38-1/483/40.886-5/8
3-1/2987/817-1/4
410-3/487/818-1/2
513811.1210-1/2
6141211.1211-1/2
816-1/2121-1/81.2513-3/4
1020161-1/41.3817
1222201-1/41.3819-1/4
1423-3/4201-3/81.520-3/4
1627201-1/21.6223-3/4
1829-1/4201-5/81.7525-3/4
2032241-5/81.7528-1/2
2437241-7/8233
https://carbonsteelflanges.com/ansi-b16-5-class-600-flanges
Nominal Pipe Size (NPS)
(inches)		Diameter of
Flange
(inches)		No.
of
Bolts		Diameter of
Bolts
(inches)		Diameter of
Bolt Holes
(inches)		Bolt
Circle
(inches)
1/24-3/443/40.883-1/4
3/45-1/843/40.883-1/2
15-7/847/814
1-1/46-1/447/814-3/8
1-1/27411.124-7/8
28-1/287/816-1/2
2-1/29-5/8811.127-1/2
39-1/287/817-1/2
411-1/281-1/81.259-1/4
513-3/481-1/41.3811
615121-1/81.2512-1/2
818-1/2121-3/81.515-1/2
1021-1/2161-3/81.518-1/2
1224201-3/81.521
1425-1/4201-1/21.6222
1627-3/4201-5/81.7524-1/2
1831201-7/8227
2033-3/42022.1229-1/2
2441202-1/22.6235-1/2
https://carbonsteelflanges.com/ansi-b16-5-class-900-flanges
Nominal Pipe Size (NPS)
(inches)		Diameter of
Flange
(inches)		No.
of
Bolts		Diameter of
Bolts
(inches)		Diameter of
Bolt Holes
(inches)		Bolt
Circle
(inches)
1/24-3/443/40.883-1/4
3/45-1/843/40.883-1/2
15-7/847/814
1-1/46-1/447/814-3/8
1-1/27411.124-7/8
28-1/287/816-1/2
2-1/29-5/8811.127-1/2
310-1/281-1/81.258
412-1/481-1/41.389-1/2
514-3/481-1/21.6211-1/2
615-1/2121-3/81.512-1/2
819121-5/81.7515-1/2
1023121-7/8219
1226-1/21622.1222-1/2
1429-1/2162-1/42.3825
1632-1/2162-1/22.6227-3/4
1836162-3/42.8830-1/2
2038-3/41633.1232-3/4
2446163-1/23.6239
https://carbonsteelflanges.com/ansi-b16-5-class-1500-flanges
Nominal Pipe Size (NPS)
(inches)		Diameter of
Flange
(inches)		No.
of
Bolts		Diameter of
Bolts
(inches)		Diameter of
Bolt Holes
(inches)		Bolt
Circle
(inches)
1/25-1/443/40.883-1/2
3/45-1/243/40.883-3/4
16-1/447/814-1/4
1-1/47-1/4411.125-1/8
1-1/2841-1/81.255-3/4
29-1/4811.126-3/4
2-1/210-1/281-1/81.257-3/4
31281-1/41.389
41481-1/21.6210-3/4
516-1/281-3/41.8812-3/4
619822.1214-1/2
821-3/41222.1217-1/4
1026-1/2122-1/22.6221-1/4
1230122-3/42.8824-3/8
https://carbonsteelflanges.com/ansi-b16-5-class-2500-flanges
If you don’t know so much, then you can continue reading.

Understanding Flange Bolt Hole Diameter

The bolt hole diameter in flanges is used to connect the different parts of a piping system. The integrity and reliability checking of a flange connection are absolutely dependent on a bolt hole diameter. Let’s discuss more about bolt hole diameter and its importance:

Importance of Flange Connections:

    The diameter of the bolt hole directly influences the strength and stability of the flange connection. It indicates the size of the bolts to be used and generally influences the clamping force applied to join the flange components. A correctly sized diameter of a bolt hole creates uniform force distribution, minimizing stress concentration and possible leakage points.

    Factors Affecting the Bolt Hole Diameter Determination

      Various factors influence the diameter of the bolt holes in a flange. These are:

      • Flange Material: Mechanical properties such as strength and ductility differ among different materials, thus the size of bolt hole diameter differs.
      • Operating Conditions: The temperature, pressure, and corrosive environment are some of the factors that influence selecting an appropriate diameter for a bolt hole that will give good performance and ensure safety in the long run.
      • Load Requirements: The magnitude of the load and the type of service that is required, whether static or dynamic, and the magnitude of forces expected will determine the required bolt hole diameter.

      Standards and Specifications of Flange Bolt Holes

      Generally, various standards and specifications imposed by industries ensure consistency, reliability, and compatibility while defining the diameter of a bolt hole for flanges. Here are some of the commonly used standards:

      American Society of Mechanical Engineers:

      The ASME B16.5 specifications include pipe flanges and flanged fittings to show dimensions, tolerances, and markings. The recommendations for bolt hole size and pattern would depend on the class, rating, and size of a pipe. This is widely accepted and used in the United States and other countries.

      Deutsches Institut für Normung:

      DIN standards are widely recognized in Europe. DIN 2501 defines the basic dimensions, flange types, and pressure ratings of steel flanges. It also provides specifications concerning the size of bolt holes according to the nominal flange size.

      European Norm:

      The European Norm standards incorporate standards from several European countries. EN 1092-1 standardizes dimensions and pressure ratings for flanges in several materials. It gives recommendations for sizes of bolt holes and numbers of bolts for each size of flange up to the largest size where bolts of reasonable size can be accommodated and considers flange material, pressure rating, and type.

      YANHAO’s Commitment to Quality and Industry Standards

      YANHAO makes sure that during flange manufacturing, attention is taken in following the industry standards and specifications. We ensure that our products meet the highest quality and specifications for our customers. Here are a few things we do to keep our commitment: 

      Incorporating Industry Standards:

      Our company designed and manufactured products according to generally accepted standards such as ASME, DIN, and EN standards. We follow the specifications of these standards exactly in the design and manufacturing of bolt hole size and pattern. 

      Quality Control Measures:

      We have strict quality control on all flanges to make sure our products meet the specified standards and satisfy the customers. We carefully check and inspect all the processes in manufacturing, down to dimensions of the diameter for bolt holes in the flanges.

      Continuous Improvement:

      YANHAO is committed to constant improvement and the timely refreshment of industry standards. We systematically reconsider and upgrade our processes with respect to any changes or improvements that might occur in specifications related to the diameter of bolt holes.

      By sticking to industrial standards and working towards improving manufacturing processes, YANHAO has always guaranteed high-quality flanges that meet requirements. Whether it is ASME, DIN, EN, or some other relevant standard, the design of products aims to meet or beat the expectations of customers regarding performance, safety, and conformation to industry regulations. 

      Bolt Hole Diameter Calculation and Design Considerations

      There are numerous aspects to consider, including gasket type, pressure rating, and flange size, when determining the proper bolt hole diameter for flanges. The bolt hole diameter design must also take vibration, thermal expansion, and flange rotation into account. YANHAO excels in utilizing the most advanced technologies and methodologies to get precise bolt hole diameter calculations.

      Bolthole Diameter Calculation:

      Usually, bolt hole diameter is calculated by empirical formulas or industry standards guidelines. The formulas consider the flange size, pressure rating and gasket type. Their purpose is to provide enough bolt hole clearance to properly install and work.

      Importance of Considering Factors:

      • Thermal Expansion: Thermal expansion and contraction of the flanges is common because of temperature variations. It can cause flange elongation or contraction, but it can also affect bolt hole alignment. To avoid misalignment, leakage, and flange damage, it is important to account for thermal expansion.
      • Vibration: In particular, the operation of flanges can involve vibration or dynamic loads, for instance, in pipelines or machinery. Stress and fatigue on the flanged joints can be caused by vibrations and lead to a change in bolt hole alignment. Vibration effects can be mitigated and joint integrity maintained by properly designed bolt holes.
      • Flange Rotation: External forces or internal pressure can cause flanges to rotate or angular move. The bolt hole alignment can be compromised by flange rotation. Bolt hole diameter should be designed to allow for flange rotation and should provide adequate clearance.

      YANHAO’s Proficiency:

      YANHAO is concerned with the use of advanced technologies and methodologies to ensure that the calculation of bolt hole diameter is highly precise. For that, we make use of computer-aided design CAD software and finite element analysis FEA for simulating different loading conditions like thermal expansion, vibration, and flange rotation.

      These advanced tools enable YANHAO to calculate the right diameter of a bolt hole according to specific flange size, pressure rating, and gasket type. This let us design flanges for withstanding thermal stresses, vibrational forces, and possible flange rotation at the highest level of performance and longevity. 

      YANHAO is proficient in the use of advanced technology and methodology to ensure the most precise calculation of bolt hole diameter. This allows us to design and manufacture flanges for applications that have high demands from quality, performance, and compliance perspectives.

      Effects of Incorrect Bolt Hole Diameter

      Application of the wrong bolt hole diameter can cause certain bad effects, including leakages, distortion of a flange, gasket damage, and safety hazards. However, expertise from YANHAO in selecting the diameter of the bolt hole will help in assuring that the risks identified above are mitigated and provide flange solutions that are reliable and durable.

      • Leakage: When the diameter of bolt holes becomes too small, it cannot provide the required compression on the gasket material, leading to leaks. This would result in the failure of joint integrity, where leakage of potential fluid or gas could cost a lot and be hazardous to the environment and safety.
      • Flange Distortion: If the bolt hole diameter is too small, then during assembly, an excessive amount of stress and strain can be exerted onto the flange material. This may result in distortion of the flange, such as warping or bending that impairs the sealing capability of the joint and reduces the overall strength and stability of the flange.
      • Gasket Damage: Insufficient bolt hole diameter can pressurize the gasket material beyond its capacity to deform, extrude or rupture. If this occurs, you can experience gasket failure, loss of seal, and higher maintenance requirements. In addition, the gaskets become damaged, and they must be replaced often, causing downtime and higher costs.
      • Safety Risks: Using the wrong bolt hole diameter can make the system less safe. Joint leakage can lead to dangerous incidents, including fires, explosions, or the release of poisonous materials. Furthermore, flange failure or distortion due to an improper bolt hole diameter may result in structural or equipment damage as well as potential worker injuries.

      YANHAO’s experience in selecting bolt hole diameter is critical in mitigating such risks and providing reliable, long-lasting flange solutions. But our engineers know very well about the very important parameters which are needed to be understood in case of bolt hole diameter calculation.

      With our extensive range of superbly engineered flange products, we highlight YANHAO’s knowledge in choosing the appropriate bolt hole diameter. We have exhaustive methods of testing procedures and quality control measures necessary to perfect your bolt hole diameter so you get accurate sealing along with proper structural integrity. This is because we are experts in this field, we have been trusted by our satisfied global customer base and we have had successful project collaborations. If you need reliable, long-lasting flange solutions above and beyond expectations, then YANHAO is your choice.

      YANHAO goes to great lengths to determine the appropriate bolt hole diameter in which a flange will fit by considering factors like flange size, pressure rating, type of gasket, and whether any other conditions such as thermal expansion, vibration, and flange rotation may contribute. This avoids leakage, flange distortion, and gasket damage, which maintain joint integrity and reduce safety hazards.

      We commit to adopt advanced technologies and methodologies in analyzing and simulating different conditions of loading. It makes sure that all flange designs stay above the industrial standards for performance that is reliable and long-lasting. We ensure that the quality, reliability, and compliance of each and every flange solution we provide meet 

      Finally

      The use of incorrect bolt hole diameter can result in leakage, flange distortion, gasket damage, and safety hazards. YANHAO’s experience covers all critical parameters and advanced technology for bolt hole diameter selection to mitigate these risks. By doing so, our flange solutions provide the best performance, reliability, and longevity that meet the highest product and safety principles.

      Author: Lewis Liu

      Hello, my name is Lewis Liu, and I’m a professional sales engineer with over a decade of expertise in the flange fittings sector.

      I am quite informed about flange selection, installation, and maintenance. I am passionate about providing customers with the greatest solutions for keeping their pipeline systems running smoothly, safely, and dependably.

      If you have any queries or concerns concerning flange fittings for your pipelines, whether they are about selection, material choice, specification requirements, or anything else, please contact me at any time. I am dedicated to providing expert advice and assistance to help you make educated decisions and reach your objectives.

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