- SHORE A
- ±5 pts against the specified hardness
- TENSILE
- Per compound datasheet, tested to ASTM D412
Pads, Stoppers & Caps · Made to order
Rubber Oil Filler Cap — Push-In, Sealed or Vented
A moulded rubber cap that closes an oil filler neck and seals against the bore on an interference fit — tight enough not to weep, loose enough to come off with oily fingers. Supplied sealed or vented, and compounded for hot oil rather than for weather.
- HARDNESS
- 50–70 Shore A, set from the removal force required
- TEMPERATURE
- −30 to +120 °C in NBR; −40 to +160 °C in AEM
- FILLER NECK BORE
- To your drawing
- INTERFERENCE
- To your specification
- VENTING
- Sealed or vented
- MADE TO ORDER
- ISO 9001:2015
- 09111526A
Product gallery
Visual Reference
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Cross section viewSection through the cap and its sealing lip — on request under NDA
- Max width
- Head diameter — to your drawing
- Thickness
- Skirt wall thickness — to your drawing
- Filler neck bore
- Diameter and depth — to your drawing
- Interference
- How far the sealing lip is oversize against the bore
- Removal force
- By hand, with oily fingers
- Venting
- Sealed, or vented with a stated flow
- Grip
- Ribbed, tabbed or plain head
Section drawing available on request. Send the filler neck bore and depth, the oil temperature at the neck and whether the cap must vent — or a sample cap and the neck it fits — and we will return a dimensioned drawing.
Technical specifications
Engineering Data
- Product Family
- Pads, Stoppers & Caps
- Material
- NBR standard; AEM where the oil runs hotter than +120 °C
- Hardness (Shore A)
- 50–70 Shore A, set from the removal force required
- Tensile Strength
- Per compound datasheet, ASTM D412
- Elongation at Break
- Per compound datasheet, ASTM D412
- Operating Temperature
- −30 to +120 °C in NBR; −40 to +160 °C in AEM
- Compression Set
- Tested to ASTM D395 Method B
- Density
- Per compound datasheet
- Colour Options
- Black standard; colour coding where several fluids share a machine
- Lead Time
- Confirmed with the quotation, from approved drawing and approved sample
- Filler neck bore
- Diameter and depth, to your drawing
- Interference
- To your specification, verified on first article
- Removal force
- To your specification, by hand
- Venting
- Sealed, or vented with a stated flow
- Medium compatibility
- Engine oil, gear oil and hydraulic fluid. Not EPDM, which swells in oil
- Grip
- Ribbed, tabbed or plain head
- Certifications
- ISO 9001:2015 — certificate 09111526A, valid to 21 February 2027
- Minimum Order
- 10,000 pieces per part number, per compound, or quoted against the part where geometry or tooling makes that unrealistic. Prototype and first-article lots sit outside the minimum.
Dimensional reference
- Max width
- Head diameter — to your drawing
- Thickness
- Skirt wall thickness — to your drawing
- Filler neck bore
- Diameter and depth — to your drawing
- Interference
- How far the sealing lip is oversize against the bore
- Removal force
- By hand, with oily fingers
- Venting
- Sealed, or vented with a stated flow
- Grip
- Ribbed, tabbed or plain head
Available materials
Rubber Compound Options
Select the compound best suited to your operating environment and application requirements.
| Rank | Compound | Temperature | Why, for an oil filler cap |
|---|---|---|---|
| Recommended | NBR | −30 to +120 °C | The standard oil-service compound and the cheapest sensible choice. Engine oil, gear oil, hydraulic fluid and the vapour above them. |
| Recommended | AEM | −40 to +175 °C continuous to +160 °C | Where the oil runs hotter than NBR can take. The step most suppliers skip, and it costs far less than FKM |
| Suitable | FKM | −20 to +250 °C continuous to +200 °C | Hot oil and aggressive fluids, at 2–3× the cost of NBR. Specify it on a measured temperature, not by default |
| Suitable | Neoprene | −40 to +120 °C | Moderate oil resistance with better weathering — useful where the filler is exposed as well as oily |
| Not recommended | EPDM | −40 to +140 °C | Swells badly in mineral oil. |
| Not recommended | SBR · natural rubber | See the compound table | No oil resistance at all |
| Available | Silicone | −60 to +220 °C | Wide temperature range, but it swells in hot mineral oil and tears easily on a part pulled off by hand |
Not sure? Send the medium, temperature and load
COMPOUND
NBR
the oil-service standard
Key advantages
Why Specifiers Choose Margo
It has to live in oil
A filler cap sits in hot oil vapour for the life of the engine. NBR is the standard answer, AEM where the oil runs hotter than +120 °C. Weather compounds swell in oil and soften — we will say so rather than quote one.
Tight enough to seal, loose enough to remove
The cap seals on an interference fit against the neck bore, and it is taken off by hand with oily fingers. Too much interference and it gets levered off with a screwdriver — then it is damaged and it leaks. We set the fit and the grip together.
Sealed or vented is not a detail
A crankcase builds pressure, and some fillers need to breathe through the cap while others must not. Fit a sealed cap where a vented one belongs and the pressure leaves through the next weakest seal — tell us which you need.
The seal is the lip, and it takes a set
A sealing lip that flattens loses its interference and starts to weep. We test compression set in-house to ASTM D395 Method B and report it, because on this part it is the difference between a cap that seals at year one and one that seals at year five.
Industries served
Global Applications
Automotive
engine, gearbox and axle fillers, and hydraulic reservoirs on commercial vehicles
Heavy industry
gearbox, compressor and hydraulic power-pack fillers on plant
Agriculture
tractor and implement transmission and hydraulic fillers, opened in the field
Pumps and valves
reservoir and gearbox fillers on process equipment
Manufacturing process
From Compound to Certification
Material compounding
Polymer blending, additive integration and batch QC in our in-house lab. The compound is chosen for oil resistance at the filler-neck temperature before anything else.
Mould Design & CNC
Mould design and CNC tool manufacture, in-house, held as a controlled record. The sealing lip and the head grip are cut together, since one sets how well the cap seals and the other whether it can be removed by hand.
Compression Moulding
Compression moulding, with the vent formed in the tool where a vented cap is specified.
Post-Cure & Trimming
Post-cure and deflashing. Flash on the sealing lip is a leak path, and flash across a vent closes it.
Quality inspection
Sealing lip diameter gauged against the neck bore, plus hardness, dimensional check and compression set on batch samples.
Export packaging
Industrial packing with documentation. Caps are bagged loose so the sealing lip is not deformed in transit. ISPM-15 treated pallets where timber packaging is used.
Quality assurance
Certified to International Standards
Every product leaves our facility with a documentation package — material test reports, dimensional inspection sheets and a certificate of conformance — giving traceability from raw material to finished part.
ISO 9001:2015 · Certificate 09111526A
Integral Certification Ltd · Valid to 21 February 2027
Scope: rubber moulded components — this part is within scope
IATF 16949 — upgrade in progress, certification targeted by end 2026
ISO 14001 and ISO 45001 — targeted 2027
Production metrics
- Since 2005
- In operation
- 60+
- Active clients
- 3–4 weeks from approved sample
- Avg. lead time
Downloads
Technical Documentation
Dimensioned drawings and standard bore sizes are issued on request, under NDA where required. Send the filler neck bore and depth, the oil temperature and whether the cap must vent, and we will confirm the fit.
Request standard bore sizesFAQ
Technical & Commercial Questions
Answers to the most common questions from engineering teams and procurement managers worldwide.
What is the minimum order quantity for this part?
We supply in bulk. The minimum run is 10,000 pieces per part number, per compound, or quoted against the part where geometry or tooling makes that unrealistic. Prototype and first-article lots sit outside the minimum.
Can you match a competitor specification or reverse-engineer an existing part?
Yes — and send the filler neck measurement, not just the cap. A cap that has been in service has swollen or set, so its dimensions are no longer the ones it was moulded to. We work from the bore it has to seal against. Tell us as well whether the old cap vented.
What file formats do you accept for drawings?
PDF, DWG, DXF and STEP. For this part the bore diameter and depth are usually enough — add the oil temperature at the neck, whether it must vent, and how much force is acceptable to remove it by hand.
Do you provide material test reports with each shipment?
Yes. Material test reports, dimensional inspection sheets and a certificate of conformance ship with every consignment. Hardness, tensile to ASTM D412 and compression set to ASTM D395 Method B are tested in-house, and the sealing lip is gauged against the neck bore on every batch.
What are your payment and delivery terms for international orders?
TT and LC accepted, discussed per order. Ex-works Nashik or FOB Nhava Sheva. Commercial invoice, packing list and certificate of origin are issued with every consignment. Caps ship bagged loose so the sealing lip is not deformed.
Same compound
Other parts we mould in the same compounds
- FKM Rotary Shaft Seals — Heat, Fuel and Aggressive Chemistry · FKM
- NBR Rotary Shaft Seals — the Standard Oil Seal · NBR
- AEM Insulation Bush — High-Temperature · AEM
- Rear Windscreen Glazing Rubber — SUV Platform · Neoprene
- Plunger Seals & Plunger Cups — Moulded for the Fluid You Pump · NBR, AEM, FKM, Neoprene
- Oil Filler Cap O-Rings — Moulded to ISO 3601 Sizes · NBR, AEM, FKM
Need this part quoted?
Send the filler neck bore and depth, the oil temperature at the neck, and whether the cap must vent. We confirm compound, interference and removal force, then quote against your annual quantity. We respond within 48 hours.