Bolt Pattern Lookup

ASME B16.5 Flange Bolt Circle, Bolt Count, and Hole Dimensions

Use this tool to quickly look up bolt pattern details for ASME B16.5 flanges. Select a nominal pipe size (NPS) and pressure class to see the number of bolts, bolt diameter, bolt circle diameter, bolt hole diameter, and key flange dimensions.

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How to Use

Select a nominal pipe size (NPS) from the first dropdown and a pressure class from the second dropdown. The tool will instantly display the bolt pattern and flange dimensions for that combination based on ASME B16.5 data.

If a particular NPS and class combination is not covered by ASME B16.5, the tool will indicate that no data is available.

Understanding Bolt Patterns

A flange bolt pattern defines how bolts are arranged around the flange face to create a pressure-tight joint. Key dimensions include:

  • Number of Bolts — the total quantity of bolts required for the flanged connection. Larger pipe sizes and higher pressure classes require more bolts.
  • Bolt Diameter — the nominal size of each bolt (stud or machine bolt) used in the connection.
  • Bolt Circle Diameter — the diameter of the imaginary circle that passes through the center of each bolt hole. This is a critical dimension for flange alignment.
  • Bolt Hole Diameter — the diameter of each hole drilled in the flange for the bolts to pass through. Bolt holes are slightly larger than the bolt diameter to allow for alignment.

Related References

  • Bolt Charts — Complete flange bolt charts with torque and bolt lengths
  • Flange Dimensions — ASME B16.5 flange outside diameter and thickness tables
  • Flange Torque — Recommended bolt torque values for flanged joints
  • Flange Types — Guide to weld neck, slip-on, blind, and other flange types