How to Choose Hydraulic Seal Kits by Size?

Ever ordered a seal kit, only to realize it doesn’t match your cylinder size? I’ve done that more than once—and it cost me time, money, and client trust.

Hydraulic seal kits by size are designed to match specific bore and rod diameters. Choosing the right kit ensures a proper fit, avoids downtime, and protects your system from leaks or damage.

Finding the right kit shouldn’t feel like a guessing game. In this article, I’ll break down exactly how to choose seal kits by size, what components to expect, and how to avoid costly mismatches.

What is included in a hydraulic seal kit?

I used to think a seal kit meant "just the seal." Turns out, a complete kit often includes 4 to 6 essential parts, all matched to the groove size and motion type.

A standard kit for a piston cylinder includes:

• Rod seal (e.g. UN Seal)
• Piston seal (e.g. KDAS Compact Seal)
• Dust wiper
• Guide band (e.g. Guide Ring)
• Backup ring or wear ring (optional)

For high-pressure or shock-load systems, kits may include a buffer seal, such as KDAS, which handles spikes and keeps the rod seal from blowing out.

Understanding what you’re buying prevents under-specing your system—and spares you emergency repair calls later.

How do I match a seal kit to my cylinder size?

Matching by size sounds simple—until you’re holding a worn-out rod with no documentation. That’s where I used to get stuck.

The right way is to measure:

• Bore diameter
• Rod diameter
• Groove depth and width (if possible)

Then match to a kit designed for that bore/rod combination. For example, a 63 mm bore with 35 mm rod might use:

• UN Rod Seal 35x45x7
• KDAS Piston Seal 63x75x8
• FA Dust Wiper 35x43x6

We group our kits by bore & rod to make this easy:
👉 View Seal Kits by Size

If you’re unsure, I always tell clients: send us a photo or drawing—we’ll match it within hours.

Are standard kits better than custom kits?

I used to swear by custom kits—until I realized that 80% of repairs can be solved with standardized sets.

Standard kits are faster to ship, often cheaper, and suitable for most construction or industrial cylinders. They work well with:

• Excavators (Komatsu, Hitachi)
• Forklifts
• Loaders
• Injection molding machines

However, if your cylinder was modified, or it’s from a rare brand, custom may be your only choice.

Here’s how I recommend deciding:

In my experience, if you service 10+ cylinders a week, stocking standard kits in sizes like 40/22, 63/35, 100/55 will save you hours.

Can one kit fit multiple machines?

The short answer: sometimes, yes.

If two machines use cylinders with the same rod and bore sizes, they likely use the same seals. That’s why we label our kits by size, not just by machine brand.

But seal profiles may still vary. A Komatsu may use a UN seal, while a similar Volvo might need a UHS. Always check groove details.

For rebuilders or repair shops, I recommend offering clients kits based on size, with an option to custom-match when specs aren’t standard.

We’ve worked with dozens of importers who started with just 3 kits—and scaled up after matching to local equipment.

Conclusion

Choosing the right hydraulic seal kit starts with knowing your sizes—and ends with reliable sealing. Whether you’re in maintenance or distribution, kits by size just make sense.

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