ASME B16.5 Flange Bolting Quick Reference

Stud size, stud length, and nut wrench size by flange class and NPS 

How to Use This Chart 

This quick reference covers the six standard ASME B16.5 pressure classes (150 through 2500) for NPS ½" to 24" raised-face (RF) flanges. For each combination of pipe size and pressure class, the table gives: 

   •  Number of stud bolts required for the pair of flanges 

   •  Stud bolt diameter (nominal) 

   •  Stud bolt length including two heavy hex nuts — for raised-face flanges 

   •  Wrench size (flat-to-flat) for the heavy hex nuts 

Key notes: 

   •  Stud bolt lengths per ASME B16.5-2020 Tables 7C, 10C, 15C, 17C, 19C, and 21C. Length includes two heavy hex nuts but excludes end-point chamfer length. 

   •  Lengths shown are for raised face: 1/16" (0.06") RF for Class 150 and 300; 1/4" (0.25") RF for Class 600, 900, 1500, and 2500. 

   •  Class 900 NPS ½ through 2½ use Class 1500 dimensions per B16.5. 

   •  Class 2500 is available only in NPS ½ through 12 per B16.5. 

   •  Wrench sizes are for standard heavy hex nuts per ASME B18.2.2. Always verify against project specifications. 

Class 150  NPS ½ – 24  |  0.06 in raised face 

Class 300  NPS ½ – 24  |  0.06 in raised face 

Class 600  NPS ½ – 24  |  0.25 in raised face 

Class 900  NPS ½ – 24  |  0.25 in raised face  |  NPS ½–2½ use Class 1500 dimensions 

Class 1500  NPS ½ – 20  |  0.25 in raised face 

Class 2500  NPS ½ – 12  |  0.25 in raised face 

References and Disclaimer 

Data is sourced from ASME B16.5-2020 Pipe Flanges and Flanged Fittings (NPS ½ through NPS 24) and MY Engineering Bolting Table v1.0. This chart is intended as a field reference only. Always verify stud bolt lengths and nut dimensions against the applicable project specifications, engineering drawings, and the current edition of ASME B16.5 before purchasing or installing hardware. For ring-joint (RTJ) or male-and-female (M&F) facings, stud lengths will differ from the raised-face values shown.