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What sizes are available for BX ring joint gaskets? This is one of the first questions oil and gas procurement professionals ask when a wellhead, Christmas tree, or manifold flange enters the maintenance cycle. The short answer is that BX ring joint gaskets are manufactured in the API 6A series from BX-150 through BX-172, covering nominal bore sizes from about 1 13/16 inches up to 21 1/4 inches. But the practical answer requires more than a list. Each BX designation ties to a specific outside diameter, ring height, groove geometry, and pressure class, and a mismatch of even a few thousandths of an inch can cause a leak during hydrostatic testing or, worse, during production. Buyers often waste days sending multiple RFQs because flange drawings are unclear or inventory data is incomplete. Ningbo Kaxite Sealing Materials Co., Ltd. solves this by supplying the full standard BX size range, with CNC-machined tolerances that match API 6A requirements, and by helping customers verify the right size before ordering. In this guide, you will see how BX sizes map to flange bores, what material and hardness values work for high-pressure service, and how to specify the correct gasket the first time.
Imagine a buyer at a gas processing plant receiving a BX-154 gasket that should fit a 4 1/16-inch 15,000 psi flange. The bag label looks right, but the outside diameter is 0.020 inches undersized because it was copied from an older API 6A edition. During pressure testing, the gasket does not energize fully against the ring groove walls, and the joint weeps. The resulting shutdown erodes the cost savings of the entire purchase.
This is not rare. BX ring joint gaskets rely on metal-to-metal contact under high bolt load. The controlled interference between the gasket and the groove creates a pressure-energized seal. If the size is wrong, no amount of torque can fix it. For procurement teams, the first layer of protection is a clear dimensional specification. The second is a supplier that understands API 6A tolerances and can confirm dimensions before shipment. Ningbo Kaxite Sealing Materials Co., Ltd. applies both layers: we check each BX size against the current API 6A standard and your flange drawing, then machine or match inventory to the correct outside diameter, height, and angle.
Below is a quick reference for common BX sizes that buyers frequently request. Use it as a starting point, but always verify the ring groove OD from your flange drawing before issuing a PO.
| BX Size | Typical Nominal Bore (in) | Common Pressure Rating (psi) | Outside Diameter Reference (in) |
|---|---|---|---|
| BX-150 | 1 13/16 | 15,000 | 2.844 |
| BX-151 | 2 1/16 | 15,000 | 3.008 |
| BX-152 | 2 9/16 | 15,000 | 3.334 |
| BX-153 | 3 1/16 | 10,000 / 15,000 | 3.974 |
| BX-154 | 4 1/16 | 10,000 / 15,000 | 4.600 |
| BX-155 | 5 1/8 | 10,000 / 15,000 | 5.746 |
| BX-156 | 7 1/16 | 10,000 / 15,000 | 7.975 |
| BX-157 | 9 | 10,000 / 15,000 | 9.475 |
| BX-158 | 11 | 10,000 / 15,000 | 11.175 |
The standard BX Ring Joint Gasket range runs from BX-150 to BX-172. That covers nominal bore sizes from 1 13/16 inches to 21 1/4 inches. The BX designation itself does not directly state the flange bore; it refers to a geometric family with a specific outside diameter, pitch diameter, and height. This often confuses buyers who are more familiar with R-type ring gaskets, where an R number often aligns more visibly with the pipe size. With BX gaskets, a given flange bore can map to one or more BX numbers depending on the flange type, pressure rating, and API 6A edition.
For example, a 2 1/16-inch 15,000 psi API 6A flange may call for a BX-151 in some connector designs, but other designs at the same bore and pressure use a BX-152. The difference lies in the ring groove outside diameter and the groove width. That is why Kaxite always asks for the flange drawing or the API 6A designation before confirming a size.
If you do not have a drawing, our team can help you identify the correct size using the groove OD and the flange bore. We also supply custom BX gaskets for proprietary flanges, older API editions, and non-standard high-pressure connections. This removes the single most common procurement bottleneck: the back-and-forth over which BX size actually fits.
Scene: A refinery maintenance buyer orders a BX-155 in carbon steel because the datasheet says “carbon steel,” but the service contains H2S and the gasket hardness exceeds NACE MR0175 limits. The gasket passes dimensional inspection but fails material compliance, and the entire lot is rejected.
The solution is to specify both size and material hardness in the same RFQ. BX ring joint gaskets are commonly supplied in soft iron, low-carbon steel, 316 stainless steel, duplex stainless steel, and Inconel 625 or 718. The material must be softer than the flange ring groove so the gasket deforms without damaging the flange. For sour service, hardness is usually limited to 22 HRC or lower, depending on the specification. At Ningbo Kaxite Sealing Materials Co., Ltd., we stock standard sizes in multiple materials and can supply mill certificates that show heat numbers, chemical composition, and hardness values.
| Material | Typical Hardness Max | Common BX Sizes Available | Service Notes |
|---|---|---|---|
| Soft Iron | 56 HRBW / 90 HRB | BX-150 to BX-172 | General oilfield service |
| Low-Carbon Steel | 68 HRBW / 90 HRB | BX-150 to BX-172 | Sour service with NACE |
| 316 Stainless Steel | 160 HV / 83 HRB | BX-150 to BX-172 | Corrosive media |
| Inconel 625 | 170 HV / 86 HRB | All sizes on request | High temp and sour service |
A purchasing manager at an offshore drilling contractor once told us: “We do not pay for the gasket. We pay for the confidence that it will not fail during a 15,000 psi test.” That confidence comes from tight dimensional control. If the outside diameter is too large, the gasket will not enter the ring groove. If it is too small, the gasket will not pressure-energize. If the angle is off by a fraction of a degree, the contact stress distribution changes and the seal may leak at high pressure.
The solution is to treat BX gasket dimensions as critical-to-quality parameters, not approximate references. At Ningbo Kaxite Sealing Materials Co., Ltd., each BX ring joint gasket is inspected for outside diameter, height, angle, and surface finish before packing. We can also provide a dimensional inspection report with every batch, which makes incoming QC easier for your team.
| Parameter | Typical API 6A Expectation | Kaxite Inspection Practice |
|---|---|---|
| Outside diameter tolerance | ±0.005 in | 100% measurement on calibrated instruments |
| Height tolerance | ±0.004 in | Sample inspection per production lot |
| Surface finish | 63 Ra max | Visual and profilometer check |
| Hardness variation | Within 10 HB across the ring | Brinell or Rockwell test per heat |
Question: What sizes are available for BX ring joint gaskets?
Answer: Ningbo Kaxite Sealing Materials Co., Ltd. supplies the full API 6A BX series from BX-150 through BX-172 as standard inventory. This range covers nominal bore sizes from 1 13/16 inches to 21 1/4 inches. We also manufacture custom BX sizes for proprietary wellhead and Christmas tree flanges. Each gasket is machined to API 6A dimensional tolerances and is traceable to a heat number.
Question: What sizes are available for BX ring joint gaskets if my flange is not a standard API 6A bore?
Answer: If your flange drawing shows a non-standard groove diameter or height, Kaxite can machine a custom BX-style gasket to your exact dimensions. We request the groove OD, groove width, and flange bore. Our engineers will recommend the correct gasket height and hardness so the seal pressure-energizes without exceeding flange stress limits.
Procurement teams often deal with suppliers that treat BX gaskets as a commodity and simply ship whatever code is on the PO. That creates risk because the same BX number can have different interpretations across API editions and flange manufacturers. Ningbo Kaxite Sealing Materials Co., Ltd. takes a different approach: we make sizing review part of the order process. Before production, our team checks your flange drawing, confirms the BX designation, and verifies material and hardness requirements. After production, we can supply dimensional inspection reports and material certificates. This reduces the chance that your BX ring joint gasket will fail during hydrotesting or installation.
We also keep a large inventory of standard BX sizes, so lead times are shorter for common BX-150 through BX-168 items. For larger BX-169 to BX-172 or special materials, we schedule production quickly and communicate clear delivery dates. Whether you need a single gasket for a repair or a full batch for a wellhead project, the goal is the same: no sizing surprises.
Need to confirm a BX size right now? Send us your flange drawing and required material. Our team will reply with the correct API 6A designation, price, and lead time.
Ningbo Kaxite Sealing Materials Co., Ltd. is a specialized manufacturer and supplier of high-performance sealing products, including the full API 6A BX ring joint gasket range from BX-150 to BX-172 and custom non-standard sizes. Our production process is built around dimensional accuracy, material traceability, and fast response to procurement teams worldwide. Learn more at https://www.kaxite-sealing.net or contact our sales team directly at [email protected] for a same-day quotation.
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