Japanese Industrial Seals: Finding Replacements for NOK, Sakagami and Machine Tool Seals

A Japanese seal rarely arrives with a tidy identity. It turns up as a worn ring in a bag, a line on a machine-tool spare parts list, or a stamped code nobody in the maintenance office recognises. The dimensions look metric and familiar — and that familiarity is exactly what causes the wrong seal to be fitted. This article sets out how Japanese industrial seals are designated, why nominal dimensions are an insufficient basis for substitution, and the procedure we use at Sealparts to identify a sealing requirement from whatever evidence is available.

1. The Japanese seal identification problem

Japanese sealing components reach the UK by two routes. The first is installed equipment: machine tools, injection moulding machines, presses, industrial vehicles, robots and hydraulic power units built in Japan and still in service decades later. The second is OEM design work where a Japanese profile was specified originally and the groove has never been changed. In both cases the person needing the seal is usually working backwards from a failure, not forwards from a drawing.

The difficulty is not that Japanese seals are exotic. It is that the Japanese sealing industry developed its own designation systems, its own profile geometry and its own housing standards in parallel with the European and American ones. Two seals can share an inside diameter, an outside diameter and a width, and still differ in lip angle, spring position, heel geometry, rubber compound and intended pressure direction.

2. Why Japanese industrial seals can be difficult to replace

Cross-referencing fails for structural reasons, not because the information is hidden:

• Profile before dimension. Japanese hydraulic catalogues are organised by profile family first (piston packing, rod packing, wiper, buffer, bearing) and by size second. A dimension alone does not tell you which family the original belonged to.
• Groove standards differ. Many Japanese hydraulic profiles are dimensioned to grooves defined by the manufacturer's own catalogue, or to JIS gland series. A European profile intended for an ISO 5597 or ISO 6547 housing will not necessarily sit correctly in them.
• Materials are named by compound, not by polymer. Sakagami compounds such as RN906 or RN919 are NBR grades with specific hardness, modulus and swell behaviour. "NBR 70" is a family, not an equivalent.
• Pressure direction is designed in. Single-acting hydraulic profiles are asymmetric. Fitting one reversed, or replacing it with a symmetric profile, changes the whole pressure balance of the gland.
• Set combinations. Japanese cylinder glands are often specified as a system — rod packing plus buffer plus wiper plus bearing ring. Replacing one element with a different profile can overload another.

3. NOK industrial seals

NOK Corporation is Japan's dominant oil seal manufacturer and the reference point for rotary shaft sealing on Japanese equipment. NOK's oil seal catalogue (Cat. No. 014E) sets out the type designations that appear on the vast majority of Japanese rotary seals, together with housing and shaft design guidance and surface roughness notation to JIS B 0601.

NOK oil seal type codes

NOK type codes are compositional rather than arbitrary: the letters describe construction and lip arrangement, so the code itself is evidence about the original design intent.

NOK also publishes housing and shaft design data — bore chamfer, shaft lead-in, hardness and surface roughness. On worn equipment this matters more than the seal choice: a shaft that has been polished below the recommended roughness band, or has a wear groove at the lip track, will leak regardless of which seal is fitted.

NOK's activity extends well beyond oil seals into hydraulic and pneumatic packings, O-rings and bonded products. Where a Japanese hydraulic component carries an NOK marking, treat the marking as a starting point for interrogation rather than a size code.

4. Sakagami hydraulic and pneumatic seals

Sakagami Seisakusho is a specialist hydraulic and pneumatic packing manufacturer whose profiles appear throughout Japanese cylinders, presses, injection moulding machines, industrial vehicles and robots. Its catalogue is organised by function, with each profile family given a short alphabetic designation and a standard compound.

Two features of the Sakagami system are worth noting for anyone cross-referencing. First, catalogue pages specify the groove, not just the seal: groove width, radii, chamfer angle, hard-chrome plated and buffed rod finishes (typically in the region of 1.6S), and the direction of pressure. Second, many families are explicitly made-to-order and quoted by part number, which means an apparently unavailable seal is often a manufacturing question rather than a stock question.

Sakagami also publishes selection guidance by operating condition — pressure bands from below 1 MPa up to 50 MPa — which is a more reliable route to a correct profile than dimension matching. See our Sakagami profile summary and Sakagami compound reference.

5. Japanese seals in machine tools

Japanese machine tools — Yamazaki Mazak, DMG MORI (Mori Seiki), Okuma, Makino and others, together with Fanuc drives and controls — have long service lives and are routinely rebuilt in the UK. Their sealing content is unglamorous but critical: spindle and gearbox oil seals, hydraulic chuck and tailstock cylinder packings, counterbalance cylinders, way lubrication seals, coolant exclusion and rotary unions.

The recurring problem in rebuild work is that the OEM spare parts list gives a machine-tool part number, not a seal designation. That number is an internal reference to a bought-in component; it will not appear in any seal manufacturer's catalogue. Identification therefore has to proceed from the physical component and the housing.

6. Why dimensions alone are insufficient

Given a used seal, the measurable dimensions are the least reliable data available. Elastomers take a compression set, swell in some fluids, shrink after thermal ageing, and deform permanently on removal. A rod packing measured after ten years in service can read one to two per cent away from its nominal size in either direction.

Even with correct nominal dimensions, functional equivalence depends on a longer list:

7. Understanding part numbers and markings

Four different kinds of number get quoted to us as "the part number". Separating them is usually the single most productive step in an identification.

1. Manufacturer series or profile designation — e.g. an NOK oil seal type letter group, or a Sakagami profile family. This identifies geometry and intended function.
2. Dimensional description — the numeric portion, normally shaft/rod × bore × width in millimetres. Useful only once the profile is known.
3. OEM machine part number — the number in the machine builder's spare parts list. It maps to a seal only through the builder's own records.
4. Distributor or internal reference — a stockist's catalogue code. It has no engineering meaning outside that organisation, and it is the most common source of bad cross-references.

8. Exact replacement versus equivalent replacement

We work down this hierarchy, and stop at the highest level that can be justified.

Level 3 is where most industrial work actually lands, and it is where the largest mistakes are made. An equivalent is equivalent for a stated duty. Change the fluid, the pressure or the temperature and the equivalence lapses.

9. How to identify an unknown Japanese seal

1. Photograph before cleaning. Markings are often ink or shallow moulded text that solvent removes. Take the photograph first.
2. Record every character. Including letters that look like noise — spring codes, cavity numbers and material suffixes carry meaning.
3. Classify the profile. Rotary lip seal, rod packing, piston packing, wiper, buffer, bearing ring or O-ring. Photograph the cross-section — cut a scrap seal in half if you have a spare.
4. Establish pressure direction. Note which face was towards pressure before the seal is removed, and photograph the gland assembled if possible.
5. Measure the hardware, not the seal. Rod or shaft diameter, bore diameter, groove diameter, groove width and any chamfer. Hardware does not take a compression set.
6. Measure the seal as corroborating evidence. ID, OD, height and lip position — recorded as measured, with a note that it is a used part.
7. Capture the duty. Fluid, pressure, temperature, speed, duty cycle and what failed.
8. Capture the machine. Builder, model, serial number and the OEM spare part number if one exists.

Groove dimensions are the most valuable measurements on the list. Given an accurate groove, a profile family and a duty, a correct seal can be specified even when the original designation is permanently lost.

10. What to send Sealparts

Send whatever you have. In order of usefulness:

• Clear photographs of the seal, including any markings and the cross-section
• Every marking transcribed exactly, including partial characters
• Rod/shaft diameter, bore diameter, groove diameter and groove width
• Seal ID, OD and width as measured, noted as a used part
• Fluid, operating pressure, temperature range and speed
• Machine builder, model, serial number and OEM spare part number
• Whether the gland is a one-piece or split groove
• A photograph or sketch of the assembled gland if it can be obtained

Our position is straightforward: if you know the part number, we can investigate it; if you do not, give us the evidence needed to identify the sealing requirement. Start with the technical enquiry form, or search our Sakagami catalogue and O-ring tooling database directly.

Conclusion

Japanese industrial seals are not harder to source than any other specialist component; they are harder to identify. The designations are systematic, the catalogues are published, and the groove data exists. What defeats most substitutions is the assumption that a metric dimension in a Japanese gland means the same thing as the same metric dimension in a European one. Interrogate the application first, the marking second, and the tape measure last.