Seal It Right the First Time – Koenig Expander® Solutions for Aerospace Applications

by Bernard Martin

If you've worked on any aerospace project, you know there’s no room for error—especially when it comes to fluid or pressure systems. One tiny leak can ground a plane or compromise an entire hydraulic manifold. That’s where the Koenig Expander® comes in. It’s one of those quietly brilliant components that makes life easier for engineers and machinists alike—no threads, no sealants, no drama.

At Factory Tooling Solutions, we represent Boneham Metal Products (BMP), the North American source for Koenig Expanders. If you’re sealing off cross-drilled holes in a high-pressure aerospace system, this is your plug-and-play solution—literally.

What Makes Koenig Expanders So Useful?
These little plugs are genius. They expand radially to seal holes by driving a precision pin into a metal sleeve—done. No tapping threads. No applying messy sealants. Just a quick press-fit that locks in place and holds tight, even under brutal pressure or extreme temps.

They’re perfect for:

• Sealing off unused ports in hydraulic manifolds
• Plugging cross-holes in actuator housings
• Simplifying compact fuel and cooling systems
• Aerospace engine blocks, gearboxes, avionics, and more

If you’ve been wrangling with pipe plugs or trying to RTV your way out of sealing issues, this will feel like a breath of fresh air.

Let’s Talk Options – Which Expander Fits Where?

Here’s a quick breakdown of how each series works—and where they shine:

SK Series – Blind Holes / Push-Style Seal (Ball Bearing Activation)
The SK Series is Koenig’s most popular style and uses a push-style activation. After you drop it into the hole, you drive a ball-bearing pin down into the sleeve, expanding it outward to grip the bore and seal the passage.

• Handles up to 600 bar (8,700 psi)
• Drop it in and drive the pin—fast, simple, reliable
• Sizes from 3.0 mm to 22.0 mm
• Available in stainless steel, brass, or aluminum
• Ideal for hydraulic actuators, fuel systems, and landing gear components
• Perfect when you’ve got a blind hole and want to keep install time minimal

LK Series – Through Holes / Pull-Style Seal (Break-Off Pin)
The LK Series is built for through-hole sealing and uses a pull-style activation. When installed, the internal pin is pulled up—causing the sleeve to expand—then the pin breaks off inside the body for a flush finish.

• Rated up to 450 bar (6,500 psi)
• Press-in install—super low-profile for tight spaces
• Sizes from 4.0 mm to 12.0 mm
• Clean break-off inside means no protrusion
• Great for applications where the plug sits in the middle of a manifold or tube with limited clearance

HC Series – Max Pressure / Pull-Style (High Compression)
For applications that push pressure boundaries, the HC Series is your go-to. It also uses a pull-style internal expansion, but it’s built to withstand intense force.

• Withstands over 1,000 bar (14,500 psi)
• Ideal for deep bores, heavy-wall components, or multi-material stacks
• Designed for extreme duty environments like spaceflight, advanced defense, or next-gen jet engines

Built to Withstand Aerospace Abuse
Koenig Expanders aren’t just tight—they’re tough. They hold up in:

• Temps from -40°C to +150°C (and up to +200°C in some models)
• Aerospace fluid systems with vibration, thermal cycling, and pressure shocks
• Materials like aluminum 7075, 6061, stainless, titanium, and even aerospace polymers

You’ll also find them certified and spec’d to:

• SAE J533
• NAS 1394
• EN9100 / AS9100

Easy to Install, Easy to Trust
No special tools required—just a press and a few seconds, and you’ve got a seal rated for flight. The bore finish tolerance? H7, with surface roughness up to Ra 3.2 µm (125 µin) still performing like a champ.
That’s a big win when you’re dealing with precision-cast housings or tight machining schedules. You don’t need to baby the installation or micromanage your sealing—just drop it in, drive it, and move on.

Let’s Get You Set Up with the Right Plug
If you’re working on aerospace systems—military or commercial—chances are you’ve already run into sealing challenges. Let us help you pick the right Koenig Expander for your application. Whether it’s an off-the-shelf SK Series for a manifold or a custom HC solution for a flight control actuator, Factory Tooling Solutions and BMP have your back.

Shoot us a print, give us a call, or tell us where you're seeing leaks—we’ll help you seal it once and seal it right.

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