O-Ring Kit Guide: AS568 Assortments, Material Kits and Custom Sets
O-ring kits — assortments of multiple sizes in a single package — are essential for maintenance teams, field engineers and workshops that service a wide range of equipment. The right kit means a replacement seal is always available; the wrong kit means the one size you need is never in the box.
This guide explains the different types of O-ring kits, what to look for, how to select the right kit for your application, and how to build a custom assortment matched to your specific equipment fleet.
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Types of O-Ring Kits
Standard AS568 Assortment Kits
The most widely available O-ring kit type. Contains multiple sizes spanning the AS568 standard, typically covering the most commonly used dash numbers.
Standard AS568 kit contents typically include:
- 70 Shore A black NBR compound (the most common specification)
- Sizes from -010 through -284 (covering 0.070", 0.103" and 0.139" cross-section series)
- 2–5 pieces per size in smaller sizes; 1–2 pieces per size in larger sizes
- Sorted storage case with labelled compartments
Limitation: Standard kits contain NBR only. If your equipment requires FKM, EPDM or Silicone, a standard NBR kit will not serve those positions.
Material-Specific Kits
Single-material kits in FKM, EPDM or Silicone, covering the same AS568 size range as standard NBR kits. Used where all equipment in a facility uses the same fluid type:
- FKM kit: Chemical plants, refineries, high-temperature systems
- EPDM kit: Water treatment plants, HVAC, steam systems
- Silicone kit: Food processing, pharmaceutical, medical equipment
Metric Kits (ISO 3601)
Kits based on ISO 3601 metric sizes rather than AS568 inch dimensions. Standard in European facilities and on European-manufactured equipment. Available in NBR, FKM and EPDM.
Application-Specific Kits
Pre-selected kits designed for a specific application type:
- Hydraulic repair kit: Heavy concentration of -2XX and -3XX AS568 sizes in 70/90 Shore A NBR
- Plumbing/HVAC kit: EPDM sizes common in threaded fittings and valve bonnets
- Instrumentation kit: Small sizes (-0XX and -1XX series) for pneumatic instruments and control valves
- Aerospace kit: FKM and specialty compounds in precision-tolerance sizes
Custom Kits
Built to your specification: select sizes, quantities per size, material and hardness. Ideal for:
- Field service teams carrying spares for a known equipment list
- OEM service kit assembly
- Facilities with specific seal standards across their equipment fleet
- Maintenance departments that want to eliminate excess inventory of rarely used sizes
Kit Type Comparison
| Kit Type | Materials | Best For | Typical Piece Count | Cost Level |
|---|---|---|---|---|
| Standard AS568 | NBR | General maintenance, workshops | 170–382 | Low |
| Material-specific | FKM, EPDM, VMQ | Single-fluid facilities | 170–382 | Medium |
| Metric (ISO 3601) | NBR, FKM, EPDM | European equipment | 150–300 | Medium |
| Application-specific | Mixed | Targeted repairs | 50–150 | Medium |
| Custom | Any | Known equipment lists | Custom | Varies |
How to Select the Right Kit
Step 1: Identify Your Fluid Media
The fluid determines the material:
- Petroleum hydraulic oils, fuels: NBR
- High temperature, aggressive chemicals: FKM
- Water, steam, HVAC: EPDM
- Food, pharmaceutical: FDA-grade EPDM or Silicone
A single-material kit only works if all your sealing positions use the same fluid type. Mixed facilities often need two kits or a custom dual-material kit.
Step 2: Identify Your Size Range
Review your equipment and identify the O-ring size range actually used. Many standard 382-piece kits include very large sizes that are rarely needed while having only 1–2 pieces of the sizes used most frequently.
For hydraulic maintenance: -2XX series (0.139" CS) and -3XX series (0.210" CS) are most commonly used. A kit with extra pieces in these series is more practical than a large kit with equal quantities across all sizes.
For instrumentation: Concentrate on -0XX and -1XX series with smaller cross-sections.
Step 3: Identify Quantity Requirements
How many jobs does the kit need to cover between restocking? Assess:
- Which sizes are replaced most frequently
- How many pieces of each are needed per repair
- How long between restocking opportunities (field service vs. plant maintenance)
A field service van may need 5–10 pieces of high-frequency sizes, while a plant workshop can restock monthly and needs fewer duplicates.
Step 4: Consider Hardness Requirements
Standard kits are 70 Shore A — appropriate for most general industrial use. If your hydraulic systems operate above 160 bar, you may need 90 Shore A for high-pressure positions. Custom kits can mix hardnesses to match your actual requirements.
Step 5: Evaluate Storage and Organisation
A quality kit should have:
- Clearly labelled compartments
- Durable case that seals against dust and moisture
- Size chart printed on the lid or included as a reference card
- Logical size progression for quick identification
What to Look for in a Quality Kit
- Full material traceability: Compound certificate available on request
- Correct compound formulation: NBR with appropriate acrylonitrile content (33–34% standard)
- Dimensional accuracy: O-rings manufactured to AS568 or ISO 3601 tolerances
- Organised storage: Clearly labelled compartments; sizes easy to identify
- Quantity per size: Enough pieces in high-frequency sizes to be useful
- Shelf life documentation: Manufacturing date and recommended storage conditions
Building a Custom O-Ring Kit
For facilities with specific equipment fleets, a custom kit is more cost-effective than multiple standard kits:
- List all sealing positions across your equipment
- Identify size and material for each position
- Estimate annual consumption per size based on maintenance frequency
- Order kit quantities based on 3–6 months of consumption per size
- Choose a storage case with compartments sized for your quantity needs
We supply custom kits in any size, material, hardness and quantity combination. Provide your size list and required quantities for a custom kit quotation.
Custom Kit Checklist
| Item | Details Needed |
|---|---|
| Size list | AS568 dash numbers or ID × CS |
| Material(s) | NBR, FKM, EPDM, VMQ, etc. |
| Hardness | 70 Shore A, 90 Shore A, mixed |
| Quantities | Pieces per size |
| Tolerance class | Standard or precision (Class A) |
| Certifications | FDA, NSF, aerospace spec |
| Case type | Plastic organizer, metal case, etc. |
Frequently Asked Questions
How many O-rings are typically in a standard AS568 kit? Standard kits range from 170-piece (partial range) to 382-piece (full AS568 range). Piece count varies by how many units per size are included. A 382-piece kit typically has 1–5 pieces of each size across the full AS568 range.
Can I get a kit with both NBR and FKM sizes? Yes — a dual-material custom kit is practical for facilities where most positions are NBR but a few critical positions require FKM. Specify which sizes you need in each material.
What is the difference between an O-ring kit and an O-ring assortment? The terms are used interchangeably. Both refer to multi-size collections of O-rings in an organised storage container.
Do kit O-rings have the same quality as individually ordered O-rings? Quality O-ring kits use the same compounds and manufacturing standards as individually supplied O-rings. Specify that you require material certificates and the supplier should provide compound certificates for kit materials.
How should O-ring kits be stored? Store away from UV light, ozone sources (electric motors, fluorescent lights), heat and solvents. Ideal storage: cool (below 25°C), dark, sealed container. Shelf life of NBR in proper storage: 5–7 years. FKM: 10+ years.
Can I build a kit for a specific machine model? Yes. If you provide the make, model, and year of your equipment, we can cross-reference the sealing positions and build a kit containing exactly the sizes and materials required for that machine.