01
Weld Neck Flange
ASME B16.5 Class 300 Flange Dimensions
02
Threaded Flange
03
Slip On Flange
04
Lap Joint Flange
05
Socket Weld Flange
06
Blind Flange
Texas Flange puts out the full ASME B16.5 Class 300 (300#) flange dimensions down below, for every nominal size from 1/2" through 24". A 4" Class 300 flange, for example, got a 10.00" outside diameter and eight 0.88" bolt holes on a 7.88" bolt circle. Texas Flange been providin' ASME B16.5 (ANSI) Class 300 flanges since 1986. For drawings, go see our CAD and 3D flange drawings, or holler at us for a quote.
Published by Texas Flange, Pearland, Texas. Dimensions per ASME B16.5. Last looked over October 6, 2026.
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Class 300 (300#) flange dimensions, ASME B16.5, in inches
| Nom. Pipe Size | O | T | TJ | R | X | #/Dia of Holesa | Bolt Circle Dia | B | B2b | B3 | H | L | L2 | L3c | r | C | D | Thr |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ½ | 3.75 | 0.50 | 0.56 | 1.38 | 1.50 | 4-0.63 | 2.62 | 0.88 | 0.62 | 0.90 | 0.84 | 0.81 | 2.00 | 0.88 | 0.12 | 0.93 | 0.38 | 0.62 |
| ¾ | 4.62 | 0.56 | 0.62 | 1.69 | 1.88 | 4-0.75 | 3.25 | 1.09 | 0.82 | 1.11 | 1.05 | 0.94 | 2.19 | 1.00 | 0.12 | 1.14 | 0.44 | 0.62 |
| 1 | 4.88 | 0.62 | 0.69 | 2.00 | 2.12 | 4-0.75 | 3.50 | 1.36 | 1.05 | 1.38 | 1.32 | 1.00 | 2.38 | 1.06 | 0.12 | 1.41 | 0.50 | 0.69 |
| 1¼ | 5.25 | 0.69 | 0.75 | 2.50 | 2.50 | 4-0.75 | 3.88 | 1.70 | 1.38 | 1.72 | 1.66 | 1.00 | 2.50 | 1.06 | 0.19 | 1.75 | 0.56 | 0.81 |
| 1½ | 6.12 | 0.75 | 0.81 | 2.88 | 2.75 | 4-0.88 | 4.50 | 1.95 | 1.61 | 1.97 | 1.90 | 1.13 | 2.63 | 1.19 | 0.25 | 1.98 | 0.62 | 0.88 |
| 2 | 6.50 | 0.81 | 0.88 | 3.62 | 3.31 | 8-0.75 | 5.00 | 2.44 | 2.07 | 2.46 | 2.38 | 1.25 | 2.69 | 1.31 | 0.31 | 2.50 | 0.69 | 1.12 |
| 2½ | 7.50 | 0.94 | 1.00 | 4.12 | 3.94 | 8-0.88 | 5.88 | 2.94 | 2.47 | 2.97 | 2.88 | 1.44 | 2.94 | 1.50 | 0.31 | 3.00 | 0.75 | 1.25 |
| 3 | 8.25 | 1.06 | 1.12 | 5.00 | 4.62 | 8-0.88 | 6.62 | 3.57 | 3.07 | 3.60 | 3.50 | 1.63 | 3.06 | 1.69 | 0.38 | 3.63 | 0.81 | 1.25 |
| 3½ | 9.00 | 1.12 | 1.19 | 5.50 | 5.25 | 8-0.88 | 7.25 | 4.07 | 3.55 | 4.10 | 4.00 | 1.69 | 3.13 | 1.75 | 0.38 | 4.13 | …. | 1.44 |
| 4 | 10.00 | 1.19 | 1.25 | 6.19 | 5.75 | 8-0.88 | 7.88 | 4.57 | 4.03 | 4.60 | 4.50 | 1.82 | 3.32 | 1.88 | 0.44 | 4.63 | …. | 1.44 |
| 5 | 11.00 | 1.31 | 1.38 | 7.31 | 7.00 | 8-0.88 | 9.25 | 5.66 | 5.05 | 5.69 | 5.56 | 1.94 | 3.82 | 2.00 | 0.44 | 5.69 | …. | 1.69 |
| 6 | 12.50 | 1.38 | 1.44 | 8.50 | 8.12 | 12-0.88 | 10.62 | 6.72 | 6.07 | 6.75 | 6.63 | 2.00 | 3.82 | 2.06 | 0.50 | 6.75 | …. | 1.81 |
| 8 | 15.00 | 1.56 | 1.62 | 10.62 | 10.25 | 12-1.00 | 13.00 | 8.72 | 7.98 | 8.75 | 8.63 | 2.38 | 4.32 | 2.44 | 0.50 | 8.75 | …. | 2.00 |
| 10 | 17.50 | 1.81 | 1.88 | 12.75 | 12.62 | 16-1.12 | 15.25 | 10.88 | 10.02 | 10.92 | 10.75 | 2.56 | 4.56 | 3.75 | 0.50 | 10.88 | …. | 2.19 |
| 12 | 20.50 | 1.94 | 2.00 | 15.00 | 14.75 | 16-1.25 | 17.75 | 12.88 | 12.00 | 12.92 | 12.75 | 2.82 | 5.06 | 4.00 | 0.50 | 12.94 | …. | 2.38 |
| 14 | 23.00 | 2.06 | 2.12 | 16.25 | 16.75 | 20-1.25 | 20.25 | 14.14 | 13.25 | 14.18 | 14.00 | 2.94 | 5.56 | 4.38 | 0.50 | 14.19 | …. | 2.50 |
| 16 | 25.50 | 2.19 | 2.25 | 18.50 | 19.00 | 20-1.38 | 22.50 | 16.16 | 15.25 | 16.19 | 16.00 | 3.19 | 5.69 | 4.75 | 0.50 | 16.19 | …. | 2.69 |
| 18 | 28.00 | 2.31 | 2.38 | 21.00 | 21.00 | 24-1.38 | 24.75 | 18.18 | 17.25 | 18.20 | 18.00 | 3.44 | 6.19 | 5.12 | 0.50 | 18.19 | …. | 2.75 |
| 20 | 30.50 | 2.44 | 2.50 | 23.00 | 23.12 | 24-1.38 | 27.00 | 20.20 | 19.25 | 20.25 | 20.00 | 3.69 | 6.32 | 5.50 | 0.50 | 20.19 | …. | 2.88 |
| 22 | 33.00 | 2.57 | 2.63 | 25.25 | 25.25 | 24-1.63 | 29.25 | 22.22 | 21.25 | 22.25 | 22.00 | 3.93 | 6.43 | 5.75 | 0.50 | 22.19 | …. | 3.13 |
| 24 | 36.00 | 2.69 | 2.75 | 27.25 | 27.62 | 24-1.63 | 32.00 | 24.25 | 23.25 | 24.25 | 24.00 | 4.13 | 6.56 | 6.00 | 0.50 | 24.19 | …. | 3.25 |
Dimensions are in inches.
(a)- Bolt hole diameter 1/8 in. larger than bolt diameter. (b)- Standard bore dimensions provided. See bore chart for other wall thicknesses. (c)- This dimension is commonly associated with “true” lap joints. Industry standard is to make to the slip on length through the hub.
Questions Folks Ask Us
- What kinda pressure can a Class 300 flange handle?
- An ASME B16.5 Class 300 flange in A105 carbon steel is rated to 740 psi at 100°F. Dat "300" is just a class designation, not the workin' pressure, and the rating falls as the temperature rises, down to 605 psig at 500°F (ASME B16.5-2025, Material Group 1.1). Y'all always make sure to confirm the pressure-temperature rating for your specific material grade.
- What sizes do dem Class 300 flanges come in?
- ASME B16.5 covers Class 300 flanges from NPS ½" clear up to 24", and ever' one of dem sizes is right here in the table on this page. Above 24", the equivalent standard is ASME B16.47 Series A and B. Go on and see the Class 300 Series A dimension table.
- What's the difference 'tween Class 150 and Class 300 flanges?
- Class 300 is rated to 740 psi at 100°F in A105 against 285 psi for Class 150, and it gets there with a thicker, heavier flange on a larger bolt circle. A 4" Class 300 flange is 10.00" outside diameter with eight 0.88" holes on a 7.88" bolt circle; the same size in Class 150 is 9.00" outside diameter with eight 0.75" holes on a 7.50" bolt circle. The bolt patterns are not interchangeable. See the Class 150 dimension table to compare size by size.
- How many bolts does a Class 300 flange use?
- It depends on the size. ASME B16.5 bolt-hole counts are always a multiple of four, runnin' from 4 bolts on ½" through 1½" up to 24 bolts of 1-1/2" diameter, in 1.63" holes, on a 32.00" bolt circle at 24". The exact count, hole diameter and bolt circle for every size are in the Class 300 table on this page, and bolt and stud sizes are on the Texas Flange bolt chart.
- What flange types are available in Class 300?
- Class 300 is available in every ASME B16.5 type Texas Flange produces: weld neck, slip-on, blind, threaded, socket weld, and lap joint, in raised face (RF) or ring type joint (RTJ).
- What does the # symbol mean in 300# flange?
- Dat # symbol is just shorthand for pressure class, so 300# and Class 300 mean the exact same thing. It's a class designation, not a weight and not a direct pressure ratin'. A Class 300 carbon steel flange in Material Group 1.1 is rated to 740 psig at -20 to 100 degrees F, and dat ratin' falls as the temperature rises.
- What are the bolt hole dimensions for a Class 300 flange?
- Bolt hole dimensions for an ASME B16.5 Class 300 flange get set by nominal pipe size. Every size calls out a bolt circle diameter, a bolt hole diameter, and a bolt count. Take a 4 inch Class 300 flange, for example: it got 8 holes of 0.88 inch diameter on a 7.88 inch bolt circle, with a 10.00 inch outside diameter. Full bolt hole dimensions for every size from 1/2 inch through 24 inch are right there in the Class 300 dimension table on this page, and bolt and stud sizes are on the Texas Flange bolt chart.
- What's the difference 'tween Class 300 and Class 600 flanges?
- Class 600 flanges are rated for twice the working pressure of Class 300 at the same temperature. In Material Group 1.1 at -20 to 100 degrees F, Class 300 is rated to 740 psig and Class 600 to 1480 psig. From 1/2 inch through 3-1/2 inch, dem two classes share the same outside diameter and bolt circle, but Class 600 runs thicker (a 2 inch flange is 1.00 inch thick in Class 600 against 0.81 inch in Class 300). From 4 inch on up, Class 600 is bigger too: a 4 inch Class 600 flange is 10.75 inch outside diameter on an 8.50 inch bolt circle, against 10.00 inch and 7.88 inch in Class 300. Go see the Class 600 dimension tables.
- Are Class 300 flange dimensions the same as ANSI B16.5 and ASME B16.5?
- Yessir. ANSI B16.5 and ASME B16.5 are talkin' 'bout the exact same standard, so a flange called ANSI B16.5 Class 300 and one called ASME B16.5 Class 300 got the exact same dimensions. ANSI does the accreditin' and ASME puts out the standard. Dem dimensions on this page work just fine no matter which name y'all use.
