Standard bonded seals
Metal washer and molded elastomer lip for general bolted static sealing.
Static Seals
Bonded Seals Manufacturer
Bonded sealing washers for hydraulic, pneumatic and industrial connections—available in metric, BSP and KDS sizes, with custom material and dimensional review.
- Metric & BSP sizes
- NBR / FKM / custom elastomers
- Custom manufacturing review
- Samples available
42 listed sizesMetric & BSPKDS seriesDrawing or sample review
Bonded seal types
Choose by geometry, thread system or custom requirement
These categories describe common sourcing routes. Final confirmation is made from the connection, dimensions and operating duty.
Self-centering bonded seals
An inner locating lip helps position the washer concentrically during assembly.
BSP bonded seals
Bonded washers matched to common BSP hydraulic ports and fitting sizes.
View BSP sizes →Metric bonded seals
Metric PPM and KDS references for threaded industrial connections.
View metric sizes →Custom bonded seals
Non-listed dimensions, elastomers, washer metals and finishes reviewed from a drawing or sample.
Discuss a custom seal →A metal washer and elastomer seal engineered as one part
Bonded seals—also called sealing washers or Dowty-type seals—provide static sealing beneath bolt heads and threaded hydraulic connections. The metal ring limits compression and carries the clamp load; the molded elastomer lip closes the leakage path.
Self-centering versions add an inner locating feature that helps position the seal on the thread before tightening. This can make repetitive fitting assembly more consistent, particularly where the seal is difficult to hold by hand.
Use the searchable dimensions below to shortlist a standard part. If the installed seal is unmarked, send its thread, washer dimensions, a drawing or a sample for review.
Bonded seal size chart
Metric, BSP and KDS bonded seal dimensions
All values are millimetres. Letters match the usual bonded-seal drawing: inside, outside, metal thickness, washer ID and self-centering ID.
Metric series, self-centering
| Auter ref. | Metric thread size | Inside diameterC | Outside diameterA | Metal thicknessE | Metal washer IDB | ID between self-centeringF |
|---|---|---|---|---|---|---|
| 603 | PPM5 | 5.70 | 9.00 | 1.00 | 6.80 | 4.50 |
| 606 | PPM6 | 6.70 | 10.00 | 1.00 | 8.00 | 4.70 |
| 612 | PPM8 | 8.70 | 13.00 | 1.00 | 10.00 | 6.40 |
| 617 | PPM10 | 10.70 | 16.00 | 1.50 | 12.40 | 8.05 |
| 622 | PPM12 | 12.70 | 18.00 | 1.50 | 14.30 | 9.73 |
| 627 | PPM14 | 14.70 | 22.00 | 1.50 | 16.40 | 11.38 |
| 629 | PPM16 | 16.70 | 24.00 | 1.50 | 18.40 | 13.41 |
| 632 | PPM18 | 18.70 | 26.00 | 1.50 | 20.40 | 14.76 |
| 633 | PPM20 | 20.70 | 28.00 | 1.50 | 22.50 | 16.76 |
| 636 | PPM22 | 22.70 | 30.00 | 2.00 | 24.40 | 18.74 |
| 638 | PPM24 | 24.70 | 32.00 | 2.00 | 26.40 | 20.11 |
| 640 | PPM27 | 27.20 | 36.00 | 2.00 | 29.00 | 23.30 |
| 642 | PPM30 | 31.00 | 39.00 | 2.00 | 33.00 | 25.70 |
| 643 | PPM33 | 33.70 | 42.00 | 2.00 | 35.80 | 28.70 |
| 645 | PPM36 | 36.70 | 46.00 | 2.00 | 38.80 | 31.10 |
| 646 | PPM39 | 39.70 | 51.00 | 2.00 | 40.00 | 34.10 |
| 647 | PPM42 | 42.70 | 53.00 | 2.00 | 45.70 | 38.70 |
| 649 | PPM48 | 48.70 | 60.00 | 2.00 | 51.70 | 43.70 |
| 650 | PPM52 | 52.70 | 66.00 | 2.00 | 56.40 | 48.20 |
| 651 | PPM60 | 60.70 | 75.00 | 2.00 | 63.00 | 56.20 |
BSP self-centering
| Auter ref. | BSP thread size | Inside diameterC | Outside diameterA | Metal thicknessE | Metal washer IDB | ID between self-centeringF |
|---|---|---|---|---|---|---|
| 820 | 1/8 BSP | 10.37 | 15.88 | 2.00 | 11.84 | 8.26 |
| 821 | 1/4 BSP | 13.74 | 20.57 | 2.00 | 15.21 | 11.18 |
| 823 | 3/8 BSP | 17.28 | 23.80 | 2.00 | 18.75 | 14.76 |
| 825 | 1/2 BSP | 21.54 | 28.58 | 2.50 | 23.01 | 18.24 |
| 826 | 5/8 BSP | 23.49 | 31.75 | 2.50 | 34.97 | 20.60 |
| 827 | 3/4 BSP | 27.05 | 34.93 | 2.50 | 28.53 | 23.83 |
| 829 | 7/8 BSP | 30.81 | 38.10 | 2.50 | 32.29 | 27.89 |
| 830 | 1 BSP | 33.89 | 42.80 | 3.20 | 36.88 | 29.92 |
| 832 | 1 1/4 BSP | 42.93 | 52.38 | 3.20 | 45.93 | 38.45 |
| 833 | 1 1/2 BSP | 48.44 | 58.60 | 3.20 | 51.39 | 44.45 |
| 836 | 2 BSP | 60.58 | 73.03 | 3.20 | 63.63 | 56.26 |
Dimensional series: KDS
| Auter ref. | Thread size | Inside diameterD1 | Outside diameterD3 | Metal thicknessL1 | Metal washer IDB | ID between self-centeringF |
|---|---|---|---|---|---|---|
| KDS10 | M10-G1/8 | 10.30 | 16.00 | 2.50 | 13.10 | 8.30 |
| KDS12 | M12 | 12.30 | 18.00 | 3.00 | 15.10 | 10.30 |
| KDS14 | M14-G1/4 | 14.30 | 20.00 | 3.00 | 17.10 | 12.30 |
| KDS16 | M16-G3/8 | 17.00 | 24.00 | 3.00 | 19.80 | 15.00 |
| KDS18 | M18 | 18.30 | 23.90 | 3.00 | 21.10 | 16.30 |
| KDS22 | M22-G1/2 | 22.30 | 30.00 | 4.50 | 25.10 | 20.30 |
| KDS26 | M26 | 26.30 | 35.00 | 3.50 | 29.40 | 24.00 |
| KDS27 | M27-G3/4 | 27.30 | 38.00 | 3.50 | 30.40 | 25.00 |
| KDS33 | M33-G1 | 33.60 | 42.00 | 3.50 | 37.30 | 31.40 |
| KDS42 | M42-G1.1/4 | 42.40 | 49.90 | 3.50 | 46.70 | 40.40 |
| KDS48 | M48-G1.1/2 | 48.40 | 60.00 | 3.50 | 52.70 | 46.40 |
Controlled elastomer compression creates the seal
Tightening the fitting applies axial load. The metal washer supports the joint and limits over-compression, while the bonded elastomer deforms against the mating face to close the leakage path.
- Metal washer
- Carries clamp load and supports the elastomer.
- Elastomer sealing lip
- Deforms to create the sealing contact.
- Bonding area
- Joins the elastomer to the metal support ring.
- Centering lip
- Locates a self-centering design on the thread.
Engineering comparison
Bonded seal vs copper washer
Both seal static threaded joints, but they create sealing contact differently. Always follow the equipment specification where one construction is prescribed.
| Decision point | Bonded seal | Copper washer |
|---|---|---|
| Sealing mechanism | Controlled elastomer deformation | Plastic deformation of metal |
| Compression control | Metal ring supports and limits the elastomer | Depends on washer deformation and joint load |
| Media selection | Elastomer compatibility must be confirmed | Metal and media compatibility must be confirmed |
| Temperature | Limited by the selected elastomer and bond | Depends on copper grade and joint design |
| Replacement | Replace if disturbed or visibly damaged | Follow the equipment service specification |
| Typical fit | Hydraulic ports, fittings and plugs | Engine, fluid and thermal joints designed for crush washers |
Where they work
Typical bonded seal applications
Bonded seals are intended for static joints where a threaded fastener or fitting supplies controlled compression.
Hydraulic fittings
Ports, adaptors, hose connections and tube fittings where fluid must be retained at the threaded interface.
Pumps and valves
Drain plugs, pressure connections, inspection points and service ports in fluid-control equipment.
Manifolds
Compact hydraulic blocks with multiple bolted connections and limited space around the sealing face.
Mobile equipment
Static fluid connections used in construction, agricultural, mining and material-handling machinery.
Specify both the elastomer and the metal ring
The sealing lip and support washer do different jobs, so both sides of the construction should be reviewed. Media, temperature and pressure guide the elastomer choice; corrosion exposure, hardware and assembly requirements guide the washer material and finish.
| Option | Useful starting point | Confirm before selection |
|---|---|---|
| NBR | General hydraulic oil service | Fluid, temperature and outdoor exposure |
| FKM | Higher-temperature or chemically demanding service | Exact chemical and low-temperature needs |
| Carbon steel ring | General industrial fittings | Corrosion protection and coating requirement |
| Stainless steel ring | Corrosive or washdown environments | Grade, mating hardware and galvanic conditions |
Bonded seal manufacturing
From confirmed construction to inspected supply
A useful quotation fixes the washer, elastomer, bond, dimensions and inspection requirement before samples or production move forward.
01
Washer and surface specification
Metal grade, dimensions, edge condition and corrosion-protection requirement are aligned to the drawing and application.
02
Rubber compound review
NBR, FKM and alternative elastomers are considered against the stated fluid, temperature and environment.
03
Rubber-to-metal bonding and molding
Tooling and the molding route control the sealing geometry and the bond between the two materials.
04
Inspection and release
Dimensions, appearance and agreed documentation are checked against the confirmed specification.
Rubber molding workshop
Tooling and compound are confirmed against the product requirement before production.
Automated inspection
Production lots can receive dimensional or visual inspection alongside laboratory checks.
Dimensional verification
Optical and height-gauge equipment supports checks against drawings and confirmed specifications.
Why Auter
Why source bonded seals from Auter?
Commercial supply is supported by sealing experience, application review and visible inspection capability—not generic quality claims.
Established sealing supplier
Auter has supplied standard, machined and custom sealing products since 2013.
Application-led review
Dimensions, material, media, pressure and temperature are considered together before confirmation.
Standard and custom routes
Stock bonded seals, samples and non-standard requirements can be handled from one inquiry.
Inspection you can discuss
Dimensional, visual, material and environmental checks can be aligned to a specific order.
From an existing fitting to a confirmed seal
01
Identify the connection
Record the thread standard and nominal size. Do not assume two similarly sized threads share the same sealing geometry.
02
Check the sealing face
Confirm that the face is flat, clean and wide enough to support the metal ring without interference.
03
Compare dimensions
Use the table letters to compare the inside diameter, outside diameter and metal thickness with the hardware.
04
Confirm material and duty
State the media, temperature, pressure and environment so the elastomer and washer can be reviewed together.
Protect the sealing lip during assembly
- Inspect the port face and remove burrs, contamination and remnants of the old seal.
- Use a new bonded seal when the elastomer is cut, flattened, hardened or detached from the washer.
- Position the seal concentrically and keep the elastomer from catching on damaged threads.
- Follow the fitting or equipment maker’s tightening procedure; excessive compression can damage the lip.
- Check the joint after pressurization using the site’s approved safety procedure.
Bonded seal FAQ
Questions buyers and engineers ask
What is a bonded seal?
A bonded seal combines a metal washer with a vulcanized elastomer sealing lip. The washer carries the tightening load while the elastomer seals around the port or fastener.
What is the difference between a standard and self-centering bonded seal?
A self-centering bonded seal has an additional inner locating lip that helps hold the seal concentrically on the thread during assembly. The mating hardware and application still need to be checked.
Which bonded seal material should I specify?
NBR is a common starting point for hydraulic oils, while FKM is often considered for higher temperatures or different media. Final selection depends on the exact fluid, temperature, pressure and exposure conditions.
What is a Dowty seal?
Dowty seal is a widely used industry term for a bonded sealing washer. It describes the same general metal-and-elastomer construction, although dimensions and designs still need to be checked by part.
What is the difference between a bonded seal and a copper washer?
A bonded seal creates its sealing contact through controlled elastomer deformation, while a copper washer relies on deformation of the metal. The suitable choice depends on the joint, media, temperature and equipment specification.
Can bonded seals be reused?
Replacement is the safer default once a joint has been disturbed. Do not reuse a seal if the elastomer is flattened, cut, hardened, displaced or separated from the washer; follow the equipment maker’s service instructions.
Are bonded seals suitable for high-pressure hydraulic systems?
They are commonly used at hydraulic ports and fittings, but pressure capability is application-specific. Thread form, sealing face, dimensions, material, tightening method and pressure cycle must all be reviewed.
Are EPDM and HNBR bonded seals available?
Alternative elastomers such as EPDM or HNBR can be reviewed for a defined application. Send the exact media, temperature range, quantity and any approval or documentation requirement.
Which bonded seal sizes are available for BSP threads?
The BSP table on this page lists sizes from 1/8 BSP through 2 BSP. Confirm the measured hardware and full thread designation before ordering.
Can Auter review a bonded seal that is not in the size table?
Yes. Send the thread designation, inside and outside diameters, washer thickness, elastomer and quantity. A drawing, clear photo or physical sample can also support identification.
What information should I send for a quotation?
Include the Auter reference or thread size, required material, quantity, operating fluid, temperature and pressure. For an existing part, add measured dimensions or a drawing.
Bonded seal inquiry
Need a bonded seal quote?
Send the size or thread, elastomer, washer material, quantity, application, pressure, temperature, medium and annual demand. Attach or link a drawing in the message when available.