ASME B16.5 Stud Bolt Diameter, Quantity & Length Chart
This table specifies the standard quantity, diameter, and stud length of alloy and stainless steel stud bolts required for ASME B16.5 Class 150, Class 300, Class 600, Class 900, Class 1500, and Class 2500 flanges.
- Lengths apply to Raised Face (RF) and Ring Type Joint (RTJ) flange connections.
- Stud bolt lengths include height for two heavy hex nuts plus two complete exposed threads.
- Thread specifications conform to ASME B1.1 Unified Coarse Thread Series (UNC) / 8N.
ASME B16.5 Bolt & Stud Dimensions — 150 LB, 300 LB & 600 LB Flanges
| Nominal Pipe Size | 150 LB. Flanges | 300 LB. Flanges | 600 LB. Flanges | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| # Bolts or Studs | Dia of Bolts or Studs | Length of Stud (1/16 RF) | Length of Stud (RTJ) | # Bolts or Studs | Dia of Bolts or Studs | Length of Stud (1/16 RF) | Length of Stud (RTJ) | # Bolts or Studs | Dia of Bolts or Studs | Length of Stud (1/4 RF) | Length of Stud (RTJ) | |
| 1/2 | 4 | 0.50 | 2-1/4 | – | 4 | 0.50 | 2-1/2 | 3 | 4 | 0.50 | 3 | 3 |
| 3/4 | 4 | 0.50 | 2-1/2 | – | 4 | 0.63 | 3 | 3-1/2 | 4 | 0.63 | 3-1/2 | 3-1/2 |
| 1 | 4 | 0.50 | 2-1/2 | 3 | 4 | 0.63 | 3 | 3-1/2 | 4 | 0.63 | 3-1/2 | 3-1/2 |
| 1-1/4 | 4 | 0.50 | 2-3/4 | 3-1/4 | 4 | 0.63 | 3-1/4 | 3-3/4 | 4 | 0.63 | 3-3/4 | 3-3/4 |
| 1-1/2 | 4 | 0.50 | 2-3/4 | 3-1/4 | 4 | 0.75 | 3-1/2 | 4 | 4 | 0.75 | 4-1/4 | 4-1/4 |
| 2 | 4 | 0.63 | 3-1/4 | 3-3/4 | 8 | 0.63 | 3-1/2 | 4 | 8 | 0.63 | 4-1/4 | 4-1/4 |
| 2-1/2 | 4 | 0.63 | 3-1/2 | 4 | 8 | 0.75 | 4 | 4-1/2 | 8 | 0.75 | 4-3/4 | 4-3/4 |
| 3 | 4 | 0.63 | 3-1/2 | 4 | 8 | 0.75 | 4-1/4 | 4-3/4 | 8 | 0.75 | 5 | 5 |
| 3-1/2 | 8 | 0.63 | 3-1/2 | 4 | 8 | 0.75 | 4-1/4 | 5 | 8 | 0.88 | 5-1/2 | 5-1/2 |
| 4 | 8 | 0.63 | 3-1/2 | 4 | 8 | 0.75 | 4-1/2 | 5 | 8 | 0.88 | 5-3/4 | 5-3/4 |
| 5 | 8 | 0.75 | 3-3/4 | 4-1/4 | 8 | 0.75 | 4-3/4 | 5-1/4 | 8 | 1.00 | 6-1/2 | 6-1/2 |
| 6 | 8 | 0.75 | 4 | 4-1/2 | 12 | 0.75 | 4-3/4 | 5-1/2 | 12 | 1.00 | 6-3/4 | 6-3/4 |
| 8 | 8 | 0.75 | 4-1/4 | 4-3/4 | 12 | 0.88 | 5-1/2 | 6 | 12 | 1.13 | 7-1/2 | 7-3/4 |
| 10 | 12 | 0.88 | 4-1/2 | 5 | 16 | 1.00 | 6-1/4 | 6-3/4 | 16 | 1.25 | 8-1/2 | 8-1/2 |
| 12 | 12 | 0.88 | 4-3/4 | 5-1/4 | 16 | 1.13 | 6-3/4 | 7-1/4 | 20 | 1.25 | 8-3/4 | 8-3/4 |
| 14 | 12 | 1.00 | 5-1/4 | 5-3/4 | 20 | 1.13 | 7 | 7-1/2 | 20 | 1.38 | 9-1/4 | 9-1/4 |
| 16 | 16 | 1.00 | 5-1/4 | 5-3/4 | 20 | 1.25 | 7-1/2 | 8 | 20 | 1.50 | 10 | 10 |
| 18 | 16 | 1.13 | 5-3/4 | 6-1/4 | 24 | 1.25 | 7-3/4 | 8-1/4 | 20 | 1.63 | 10-3/4 | 10-3/4 |
| 20 | 20 | 1.13 | 6-1/4 | 6-3/4 | 24 | 1.25 | 8 | 8-3/4 | 24 | 1.63 | 11-1/4 | 11-1/2 |
| 24 | 20 | 1.25 | 6-3/4 | 7-1/4 | 24 | 1.50 | 9 | 10 | 24 | 1.88 | 13 | 13-1/4 |
ASME B16.5 Bolt & Stud Dimensions — 900 LB, 1500 LB & 2500 LB Flanges
| Nominal Pipe Size | 900 LB. Flanges | 1500 LB. Flanges | 2500 LB. Flanges | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| # Bolts or Studs | Dia of Bolts or Studs | Length of Stud (1/4 RF) | Length of Stud (RTJ) | # Bolts or Studs | Dia of Bolts or Studs | Length of Stud (1/4 RF) | Length of Stud (RTJ) | # Bolts or Studs | Dia of Bolts or Studs | Length of Stud (1/4 RF) | Length of Stud (RTJ) | |
| 1/2 | 4 | 0.75 | 4-1/4 | 4-1/4 | 4 | 0.75 | 4-1/4 | 4-1/4 | 4 | 0.75 | 4-3/4 | 4-3/4 |
| 3/4 | 4 | 0.75 | 4-1/2 | 4-1/2 | 4 | 0.75 | 4-1/2 | 4-1/2 | 4 | 0.75 | 5 | 5 |
| 1 | 4 | 0.88 | 5 | 5 | 4 | 0.88 | 5 | 5 | 4 | 0.88 | 5-1/2 | 5-1/2 |
| 1-1/4 | 4 | 0.88 | 5 | 5 | 4 | 0.88 | 5 | 5 | 4 | 1.00 | 6 | 6 |
| 1-1/2 | 4 | 1.00 | 5-1/2 | 5-1/2 | 4 | 1.00 | 5-1/2 | 5-1/2 | 4 | 1.13 | 6-3/4 | 6-3/4 |
| 2 | 8 | 0.88 | 5-3/4 | 5-3/4 | 8 | 0.88 | 5-3/4 | 5-3/4 | 8 | 1.00 | 7 | 7 |
| 2-1/2 | 8 | 1.00 | 6-1/4 | 6-1/4 | 8 | 1.00 | 6-1/4 | 6-1/4 | 8 | 1.13 | 7-3/4 | 8 |
| 3 | 8 | 0.88 | 5-3/4 | 5-3/4 | 8 | 1.13 | 7 | 7 | 8 | 1.25 | 8-3/4 | 9 |
| 4 | 8 | 1.13 | 6-3/4 | 6-3/4 | 8 | 1.25 | 7-3/4 | 7-3/4 | 8 | 1.50 | 10 | 10-1/4 |
| 5 | 8 | 1.25 | 7-1/2 | 7-1/2 | 8 | 1.50 | 9-3/4 | 9-3/4 | 8 | 1.75 | 11-3/4 | 12-1/4 |
| 6 | 12 | 1.13 | 7-1/2 | 7-3/4 | 12 | 1.38 | 10-1/4 | 10-1/2 | 8 | 2.00 | 13-1/2 | 14 |
| 8 | 12 | 1.38 | 8-3/4 | 8-3/4 | 12 | 1.63 | 11-1/2 | 11-3/4 | 12 | 2.00 | 15 | 15-1/2 |
| 10 | 16 | 1.38 | 9-1/4 | 9-1/4 | 12 | 1.88 | 13-1/4 | 13-1/2 | 12 | 2.50 | 19-1/4 | 20 |
| 12 | 20 | 1.38 | 10 | 10 | 16 | 2.00 | 14-3/4 | 15-1/4 | 12 | 2.75 | 21-1/4 | 22 |
| 14 | 20 | 1.50 | 10-3/4 | 11 | 16 | 2.25 | 16 | 16-3/4 | – | – | – | – |
| 16 | 20 | 1.63 | 11-1/4 | 11-1/2 | 16 | 2.50 | 17-1/2 | 18-1/2 | – | – | – | – |
| 18 | 20 | 1.88 | 12-3/4 | 13-1/4 | 16 | 2.75 | 19-1/2 | 20-3/4 | – | – | – | – |
| 20 | 20 | 2.00 | 13-3/4 | 14-1/4 | 16 | 3.00 | 21-1/4 | 22-1/4 | – | – | – | – |
| 24 | 20 | 2.50 | 17-1/4 | 18 | 16 | 3.50 | 24-1/4 | 25-1/2 | – | – | – | – |
Frequently Asked Questions
How many bolts does a flange have?
ASME B16.5 flanges always have a bolt count that is a multiple of four, from 4 bolts on small sizes to 20 or more on large diameters. The exact count, bolt size, and bolt circle depend on the nominal size and pressure class; use the chart above to look up yours.
What is the difference between a stud bolt and a machine bolt?
A stud bolt is a fully threaded rod tightened with two heavy hex nuts, and is standard for most flange connections, especially higher-pressure and critical service. A machine bolt has a fixed hex head and a single nut, and is used mainly in lower-pressure, non-critical applications.
What material are flange bolts made from?
The most common combination for carbon and alloy steel flanges is ASTM A193 Grade B7 stud bolts with ASTM A194 Grade 2H heavy hex nuts. Stainless and special-service applications use grades such as B8 or B8M. We can supply bolting to match your flange and service.
What length stud bolt do I need for a flange?
Stud length is driven by the combined thickness of the two flanges, the gasket, and the facing, plus enough thread to engage both nuts. The chart above lists standard stud lengths by size and class; tell us your gasket and facing and we will confirm.
What bolt size does a Class 150 flange use?
Class 150 bolt diameters run from 1/2" on small sizes up to 1-1/4" on a 24" flange. The chart above gives the exact diameter, count, and bolt circle for every size.
📌 Bolting Selection Notes
1. Bolt Materials: High-temperature alloy steel bolting conforms to ASTM A193 Grade B7 stud bolts with ASTM A194 Grade 2H heavy hex nuts.
2. Stainless Bolting: Corrosion-resistant applications use ASTM A193 Grade B8 (304 SS) or B8M (316 SS) with Class 1 or Class 2 strain-hardened ratings.
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