The OSK™ O-Ring Service Kit in Viton/FKM face seal configuration puts eight of the most-used SAE ORFS face seal O-Ring sizes in one latching plastic case, so a leaking flat-face fitting gets fixed today instead of next week. Every O-Ring in the kit is 90 durometer FKM (Viton®) in black, rated from -20F to +400F (-29C to +204C). It is built as a cross-reference for shops that stock Cat® kit 270-0459 and work on Caterpillar® and other mobile equipment. If you service hydraulic lines, fuel systems, or engine joints where heat and aggressive fluids eat up standard Buna-N, this is the kit that belongs on the truck. The O-Ring Store LLC ships it same day with real-time inventory, and every size in it can be reordered on its own.
Benefits
A face seal fitting only leaks at the worst time. You are halfway through a repair, the machine is down, and the one O-Ring you need is forty miles away at a parts counter. The OSK™ kit ends that. Open the case, pull the size, seat it, and get the machine back to work.
The real win is not the rubber. It is the time you stop losing. One kit on a service truck can save several hours of drive time on a single call. One kit on a maintenance shelf keeps a line running instead of sitting idle while somebody chases a two dollar seal. You also stop guessing. The sizes are separated in the case, so a tech grabs the right one the first time instead of eyeballing a handful of loose O-Rings and hoping.
Because these are FKM and not Buna-N, you get one more benefit: the kit covers the hot and aggressive jobs where a general-purpose kit would fail. Diesel, biodiesel, hot hydraulic oil, and high under the hood temperatures are all in range.
Correct Size Coverage
This kit covers eight SAE ORFS face seal sizes. Quantities are 5 pieces per size.
- ORFS -4 (1/4 in. tube), Cat® cross 4J5477, qty 5
- ORFS -6 (3/8 in. tube), Cat® cross 6V8397, qty 5
- ORFS -8 (1/2 in. tube), Cat® cross 6V8398, qty 5
- ORFS -10 (5/8 in. tube), Cat® cross 7J9108, qty 5
- ORFS -12 (3/4 in. tube), Cat® cross 6V9746, qty 5
- ORFS -16 (1 in. tube), Cat® cross 5K9090, qty 5
- ORFS -20 (1-1/4 in. tube), Cat® cross 6V8400, qty 5
- ORFS -25, Cat® cross 8T0315, qty 5
[HOLD FOR MARTY: AS568 dash number, ID, OD, and CS for each of the eight sizes are not in the source data and were not filled in. Send them and I will drop them into this list in inch and metric. See open items at the end.]
SAE, Metric, or Specialty Kit Type
This is a specialty ORFS face seal kit, not a general repair assortment and not a metric bore kit. ORFS stands for O-Ring Face Seal. The O-Ring sits in a machined groove on the flat face of the fitting and squeezes flat when the nut is tightened. That gives a leak-free joint on higher pressure hydraulic lines.
Two things this kit is not. It is not an SAE AS568 general bore kit for cylinders, pumps, and gearboxes. It is not an SAE straight thread or Boss kit for the -900 series ports. If you need those, order the right kit. A face seal O-Ring is sized for the face groove on the fitting, and it will not seal a port or a piston groove correctly.
Sizes are called out by ORFS tube size, which is the standard way flat-face fittings are ordered. Match the tube size on your fitting to the compartment in the case.
Material Compatibility
The O-Rings in this OSK™ kit are FKM, sold under the Viton® trade name. FKM is the premium high-temperature and chemical-resistant compound. It holds up at heat that would harden or crack Buna-N, and it resists a much wider list of fluids.
FKM has excellent resistance to petroleum oils, petroleum-based hydraulic fluids, gasoline, diesel, JP-8, aromatic fuels, chlorinated solvents, mineral acids, and silicone fluids. It also has low gas permeability and holds compression set well at elevated temperature, which is why it lasts in hot service.
FKM has limits you need to respect. It has limited capability with steam, hot water above 300F (149C), low-molecular-weight esters, and some ketones. It is not compatible with ketones such as MEK and acetone, amines, anhydrous ammonia, ethylene oxide, or low-molecular-weight organic acids. If your machine runs a phosphate-ester fluid or a chemical that is not plain petroleum oil or fuel, confirm before you install. For any critical job, check the compound against your actual fluid, temperature, and pressure.
Temperature range for this kit is -20F to +400F (-29C to +204C).
Durometer and Seal Performance
Durometer is how hard the rubber is on the Shore A scale. Every O-Ring in this kit is 90 durometer. That is a hard compound on purpose.
A 70 durometer O-Ring is the general-purpose choice. It is softer, seats easily, and works fine in most low and medium pressure bore seals. A 90 durometer O-Ring is stiffer and resists extrusion. Extrusion is when pressure pushes the rubber into the tiny gap at the edge of the groove and shreds it. At the pressure a hydraulic face seal fitting sees, a soft O-Ring can get chewed up and start weeping.
That is why face seal fittings call for 90 Duro. The harder body stays in the groove, holds its shape under clamp load and pressure, and gives longer service life. Putting a 70 Duro O-Ring in a high pressure ORFS fitting is a common mistake and a common repeat leak. This kit takes that mistake off the table.
Best Uses
- Hydraulic repair shops working flat-face ORFS fittings
- Service trucks and field repair on mobile equipment
- Caterpillar® and other heavy equipment maintenance
- Construction and earthmoving equipment fleets
- Farm and ag equipment repair
- Engine and fuel system service at elevated temperature
- Diesel and biodiesel fuel line joints
- Manufacturing and plant maintenance with hot hydraulic circuits
- Static and dynamic joints on mobile machines and engines
This kit is not the right pick for unknown chemicals, or for critical aerospace, medical, or highly specified work, unless the material, certification, and traceability are confirmed for your application first.
Quality and Reliability
This is a professional repair kit, not a bin of mixed rubber. Every O-Ring in it is a known compound at a known durometer in a known size. That matters more than a big piece count. A wrong-size or wrong-material O-Ring does not save you anything. It sends the machine back to the shop.
The O-Rings meet ORFS face seal requirements for flat-face fittings and are matched to the fluids, pressures, and temperatures typical of engine and mobile equipment service.
The O-Ring Store LLC runs an ISO 9001:2015 certified quality management system, and we back it with our Olypsys® quality verification system. That means the size in the compartment is the size on the label. Fewer wrong-size repairs, less wasted time, fewer callbacks on the same fitting.
Prop 65 warning: This product contains chemicals known to the State of California to cause cancer or reproductive harm, including Tetrafluoroethylene and PFOA.
Organized Storage Case
The kit ships in a rugged plastic case with a latching lid and individual compartments for each size. Each size stays separated, which does two things. It keeps dirt and shop grit off the sealing surface, and it lets a tech find the right size fast during a repair instead of sorting through a pile.
The case is sized to live in a truck box, on a shelf, or in a toolbox drawer without taking over the space.
Before You Buy
Match the O-Ring to the fitting, not to the last one you pulled out. A stretched or swollen used O-Ring will measure wrong. Check the ORFS tube size stamped on the fitting or measure the face groove.
Match the material to the job. FKM is the right call for heat, fuel, and aggressive service. It is the wrong call for steam, hot water above 300F (149C), ketones, amines, or brake fluid. If you are not sure what fluid is in the system, find out before you install.
Also check pressure and temperature against the compound, not just the size. And for any critical application, confirm material, durometer, certification, and traceability before you put it in service. Give us a call if you want a second set of eyes on it.
Why Buy From The O-Ring Store LLC
The O-Ring Store LLC is an ISO 9001:2015 certified O-Ring and seal distributor. We make getting O-Rings easy!
When you buy the OSK™ O-Ring Service Kit from us, you get more than a case of seals. You get clear sizing you can trust, straight answers about what the compound will and will not handle, same-day shipping with real-time inventory, and single-size refills so the kit keeps working for you years down the road. We also handle custom kitting, labeling, and packaging if you need a kit built to your own size list.
Behind all of that is a crew that works with O-Rings and seals every single day. Call us with a size question or a fluid compatibility question and you get a real person who knows the answer. That is the difference between buying from a catalog and buying from a seal house.
FAQ
What is this OSK™ kit used for? It is a service kit of SAE ORFS face seal O-Rings for flat-face hydraulic fittings. Shops and service trucks use it to repair leaking face seal joints on Caterpillar® and other mobile equipment without waiting on a parts order. It covers eight ORFS tube sizes with 5 O-Rings of each size.
Is this an SAE or metric kit? It is SAE. The sizes are SAE ORFS face seal sizes called out by tube size, from -4 (1/4 in. tube) through -25. It is not a metric ISO 3601 kit and it is not an SAE AS568 general bore kit.
What material are the O-Rings? FKM, also sold under the Viton® trade name, in black at 90 durometer Shore A. The temperature range is -20F to +400F (-29C to +204C).
Will these work with hydraulic oil and diesel fuel? Yes. FKM has excellent resistance to petroleum-based hydraulic fluids, gasoline, diesel, and biodiesel, and it holds up at temperatures where Buna-N hardens or fails. Do not use FKM in steam, hot water above 300F (149C), ketones, amines, or glycol brake fluid.
Why 90 durometer instead of 70? Face seal fittings run high pressure, and a soft 70 durometer O-Ring can extrude into the gap at the edge of the groove and tear. The harder 90 durometer compound resists extrusion, holds its shape under clamp load, and lasts longer in the fitting. Using 70 duro in an ORFS joint is a common cause of repeat leaks.
Can I refill the kit instead of replacing it? Yes. Every size in the kit is available from The O-Ring Store LLC as an individual size in 90 duro FKM, so you restock just the sizes you use up. You never have to buy a whole new kit because two popular sizes ran out first.
Does this replace Cat® kit 270-0459? This OSK™ kit is offered as a cross-reference for shops that use Cat® seal kit 270-0459 and covers the same eight ORFS face seal sizes in 90 duro FKM. Confirm the size and application against your machine before you install. The O-Ring Store LLC is not affiliated with Caterpillar Inc.
