Flange & Ring Gasket Lookup
API 6A/6BX bore size and pressure rating to ring gasket number, stud count, stud length and diameter, and flange OD. Filter it down to one bore or one rating, or browse the whole chart.
| Bore | Rating | Ring Gasket | Studs | Stud Length | Stud Dia. | Nut A/F | Flange OD |
|---|---|---|---|---|---|---|---|
| 1 13/16" | 10M | BX-151 | 8 | 5 1/4" | 3/4" | 1 1/4" | 7 3/8" |
| 1 13/16" | 15M | BX-151 | 8 | 5 7/8" | 7/8" | 1 7/8" | 8 3/16" |
| 1 13/16" | 20M | BX-151 | 8 | 7 3/4" | 1" | 1 5/8" | 10 1/8" |
| 2 1/16" | 5M | R-24 | 8 | 6 1/4" | 7/8" | 1 7/16" | 8 1/2" |
| 2 1/16" | 10M | BX-152 | 8 | 5 1/2" | 3/4" | 1 1/4" | 7 7/8" |
| 2 1/16" | 15M | BX-152 | 8 | 6 1/4" | 7/8" | 1 7/16" | 8 3/4" |
| 2 1/16" | 20M | BX-152 | 8 | 8 1/2" | 1 1/8" | 1 13/16" | 11 5/16" |
| 2 9/16" | 5M | R-27 | 8 | 7" | 1" | 1 5/8" | 9 5/8" |
| 2 9/16" | 10M | BX-153 | 8 | 6 1/4" | 7/8" | 1 7/16" | 9 1/8" |
| 2 9/16" | 15M | BX-153 | 8 | 7" | 1" | 1 5/8" | 10" |
| 2 9/16" | 20M | BX-153 | 8 | 9 1/2" | 1 1/4" | 2" | 12 13/16" |
| 3 1/8" | 3M | R-31 | 8 | 6 1/4" | 7/8" | 1 7/16" | 9 1/2" |
| 3 1/8" | 5M | R-35 | 8 | 7 3/4" | 1 1/8" | 1 13/16" | 10 1/2" |
| 3 1/16" | 10M | BX-154 | 8 | 7 1/4" | 1" | 1 5/8" | 10 5/8" |
| 3 1/16" | 15M | BX-154 | 8 | 8" | 1 1/8" | 1 13/16" | 11 5/16" |
| 3 1/16" | 20M | BX-154 | 8 | 10 1/4" | 1 3/8" | 2 3/16" | 14 1/16" |
| 4 1/16" | 3M | R-37 | 8 | 7 1/2" | 1 1/8" | 1 13/16" | 11 1/2" |
| 4 1/16" | 5M | R-39 | 8 | 8 1/2" | 1 1/4" | 2" | 12 1/4" |
| 4 1/16" | 10M | BX-155 | 8 | 8 3/8" | 1 1/8" | 1 13/16" | 12 7/16" |
| 4 1/16" | 15M | BX-155 | 8 | 9 1/2" | 1 3/8" | 2 3/16" | 14 3/16" |
| 4 1/16" | 20M | BX-155 | 8 | 12 1/4" | 1 3/4" | 2 3/4" | 17 9/16" |
| 5 1/8" | 3M | R-41 | 8 | 8" | 1 1/4" | 2" | 13 3/4" |
| 5 1/8" | 5M | R-44 | 8 | 10 1/4" | 1 1/2" | 2 3/8" | 14 3/4" |
| 5 1/8" | 10M | BX-169 | 12 | 9 1/4" | 1 1/8" | 1 13/16" | 14 1/16" |
| 7 1/16" | 3M | R-45 | 12 | 8 1/2" | 1 1/8" | 1 13/16" | 15" |
| 7 1/16" | 5M | R-46 | 12 | 11 1/4" | 1 3/8" | 2 3/16" | 15 1/2" |
| 7 1/16" | 10M | BX-156 | 12 | 11 3/4" | 1 1/2" | 2 3/8" | 18 7/8" |
| 7 1/16" | 15M | BX-156 | 16 | 13" | 1 1/2" | 2 3/8" | 19 7/8" |
| 7 1/16" | 20M | BX-156 | 16 | 17 3/4" | 2" | 3 1/8" | 25 13/16" |
| 9" | 3M | R-49 | 12 | 9 1/2" | 1 3/8" | 2 3/16" | 18 1/2" |
| 9" | 5M | R-50 | 12 | 12 1/2" | 1 5/8" | 2 9/16" | 19" |
| 9" | 10M | BX-157 | 16 | 13 1/4" | 1 1/2" | 2 3/8" | 21 3/4" |
| 9" | 15M | BX-157 | 16 | 15 3/4" | 1 7/8" | 2 15/16" | 25 1/2" |
| 11" | 2M | R-53 | 16 | 9 1/4" | 1 1/4" | 2" | 20" |
| 11" | 3M | R-53 | 16 | 10" | 1 3/8" | 2 3/16" | 21 1/2" |
| 11" | 5M | R-54 | 12 | 14 1/2" | 1 7/8" | 2 15/16" | 23" |
| 11" | 10M | BX-158 | 16 | 15 3/8" | 1 3/4" | 2 3/4" | 25 3/4" |
| 11" | 15M | BX-158 | 20 | 19 1/2" | 2" | 3 1/8" | 32" |
| 11" | 20M | BX-158 | 16 | 24" | 2 3/4" | — | 34 3/4" |
| 13 5/8" | 2M | R-57 | 20 | 9 1/2" | 1 1/4" | 2" | 22" |
| 13 5/8" | 3M | R-57 | 20 | 10 3/4" | 1 3/8" | 2 3/16" | 24" |
| 13 5/8" | 5M | BX-160 | 16 | 12 3/4" | 1 5/8" | 2 9/16" | 26 1/2" |
| 13 5/8" | 10M | BX-159 | 20 | 17 3/4" | 1 7/8" | 2 15/16" | 30 1/4" |
| 13 5/8" | 15M | BX-159 | 20 | 21" | 2 1/4" | 3 1/2" | 34 7/8" |
| 13 5/8" | 20M | BX-159 | 20 | 30" | 3" | — | 45 3/4" |
| 16 3/4" | 2M | R-65 | 20 | 10 3/4" | 1 1/2" | 2 3/8" | 27" |
| 16 3/4" | 3M | R-66 | 20 | 12 1/4" | 1 5/8" | 2 9/16" | 27 3/4" |
| 16 3/4" | 5M | BX-162 | 16 | 14 3/4" | 1 7/8" | 2 15/16" | 30 3/8" |
| 16 3/4" | 10M | BX-162 | 24 | 17 3/4" | 1 7/8" | 2 15/16" | 34 5/16" |
| 18 3/4" | 5M | BX-163 | 20 | 18" | 2" | 3 1/8" | 35 5/8" |
| 18 3/4" | 10M | BX-164 | 24 | 22 1/2" | 2 1/4" | 3 1/2" | 40 15/16" |
| 18 3/4" | 15M | BX-164 | 20 | 27" | 3" | — | 45 3/4" |
| 21 1/4" | 2M | R-73 | 24 | 12 1/2" | 1 5/8" | 2 9/16" | 32" |
| 20 3/4" | 3M | R-74 | 20 | 15 1/4" | 2" | 3 1/8" | 33 3/4" |
| 21 1/4" | 5M | BX-165 | 24 | 18 3/4" | 2" | 3 1/8" | 39" |
| 21 1/4" | 10M | BX-166 | 24 | 24 1/2" | 2 1/2" | 3 7/8" | 45" |
| 26 3/4" | 2M | BX-167 | 20 | 14 1/2" | 1 3/4" | 2 3/4" | 41" |
| 26 1/4" | 3M | BX-168 | 24 | 17 3/4" | 2" | 3 1/8" | 43 3/8" |
Reading the Chart
Every row is one bore-and-rating combination, because a flange's ring gasket, stud count, and stud size are all fixed the moment those two numbers are set — there's no independent choice to make once you know the bore and the pressure class.
Ring gasket number is what you order: an "R" number is a plain gasket seated in a flat groove, used up through 5M. A "BX" number is pressure-energized — wellbore pressure helps hold it sealed rather than working against it — and is standard at 10M and above, including virtually every BOP stack connection.
Studs, stud length and stud diameter are the physical bolt-up. Nut A/F is the width-across-flats for the matching heavy hex nut per ASME B18.2.2 — the number that tells you what socket to bring, not just what to order.
Why This Matters on the Floor
Nippling up or down a BOP stack, changing a spool, or reconnecting a wellhead flange all come down to the same question: does the gasket, stud, and nut set actually match the bore and rating stamped on the flange. Getting a ring gasket number wrong doesn't always fail obviously — a close but incorrect BX number can look seated and still not hold at test pressure, which is exactly why the pressure test exists as a separate check from the visual one.
For the stack this most often applies to, see how a BOP stack is arranged and where these flanged connections sit in it. Bit and drill string connections use a completely different threaded system — see the bit thread and make-up torque lookup for that side of it.
Frequently Asked Questions
What is a ring gasket number?
It is the API 6A/6BX designation stamped on the gasket itself and on the flange’s data plate — "R-24" or "BX-152", for example. The number identifies the exact gasket geometry for one bore size and pressure rating combination, so quoting the number is unambiguous in a way that "the usual one for this flange" is not.
What is the difference between an R gasket and a BX gasket?
An R gasket sits in a flat, symmetrical groove and relies on bolt-up force alone to seal — used on lower pressure classes, generally 2M through 5M. A BX gasket is pressure-energized: wellbore pressure itself pushes the ring tighter against the groove walls, which is why it is used at 10M and above and on virtually all BOP stack connections. The two are not interchangeable even at an overlapping bore size.
How do I find the right ring gasket for my flange?
Match the bore size and pressure rating stamped on the flange’s own data plate against the table. If the data plate is missing or worn, the ring groove dimensions can be measured and cross-checked against API 6A, but ordering from a measured guess rather than a confirmed rating is exactly how a mismatched gasket gets bolted up.
What does "Nut A/F" mean in the table?
Across-flats — the wrench size of the heavy hex nut that fits the stud, per ASME B18.2.2. It is listed because it is the dimension you actually need at the tool box: the stud diameter tells you what nut to order, but A/F tells you what socket or wrench fits it.
Are these dimensions the same for every manufacturer’s flanges?
API 6A standardizes the dimensions specifically so that compliant flanges from different manufacturers bolt up to each other. This table reflects Cameron’s own published figures; other API 6A-compliant manufacturers should match, but always verify against the specific flange’s data plate before ordering studs or gaskets.
Does this table apply to wellhead housings and spools too?
Wellhead housings, spools and BOP stack connections in this bore and pressure range generally use the same API 6A/6BX flange system, so the table applies. It does not cover clamp hub or other non-flanged connection types, which use a different sealing arrangement entirely.