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Industries | Aerospace & Defense | Products | Plugs

Plugs

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Aerospace and Defense Plugs

The Industry Benchmark for Expansion Plugs

The Lee Plug product line is the foundation for our extensive line of aerospace products. Back in the 1950s, engineers were searching for a more reliable and effective way to seal machined and cross-drilled holes in metal housings. In response to this need, The Lee Company created a plug designed to form a permanent leak-tight seal without the use of O-rings, threads, or sealants. The Lee Plug remains the best-seller for The Lee Company, with well over 200 million plugs having been used on aircraft, missiles, spacecraft, and other sophisticated hydraulic systems.

The Lee Plug® Expansion Plug remains the best seller for many reasons. Not only are we the original OEM and the only qualified supplier of the single-point-of-failure technology, but we also bring a level of problem-solving, experience, innovation, and a commitment to quality that sets us and the product apart from our competitors. This is why The Lee Company remains the only SAE-certified provider of aerospace expansion plugs.

Lastly, each of our customers is unique – and they often need unique plugs. Over half of the work we perform at The Lee Company is custom, and plugs are no exception. Our standard product offering usually contains a plug the size and proof pressure that a customer needs. This includes evolved configurations of our original expansion plug with different material, installation, and retention options. With that said, we’re more than happy to create new designs on request. Whether your solution is off-the-shelf or one-of-a-kind, you can rest assured knowing that Lee products always adhere to exacting standards for quality and performance.

Lee Plug® Expansion Plugs

The founding, flagship product from The Lee Company. It works like this: the cylindrical plug body contains a tapered hole partway through. The body is inserted into a properly reamed hole. A tapered pin is then inserted into the plug itself. This causes the plug to expand in a controlled manner. Lands and grooves on the side of the plug then bite into the sides of the hole, creating multiple metal-to-metal seals. See Installation Process Specification 203 (which applies to all Lee expansion plugs) for more information.

Lee Plugs are manufactured to exacting tolerances. Every process is precisely controlled. Each lot of pins and plugs undergoes a rigorous inspection and acceptance testing. This ensures performance when any failure could be catastrophic.

Standard Lee Plugs are available in multiple grades of aluminum, stainless steel, and Monel, plus titanium and MP35N. They can be purchased in diameters from 0.093 to 0.656 of an inch or metric sizes from 2.5 to 8.0 mm.

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Lee R.F.O.® (Radial Force Only) Plugs

Lee R.F.O. Plugs are designed to seal holes in thin walls or fragile materials. Designed to be easily removable, these plugs do not require a support shoulder and the installation system ensures that no downward pressure is applied to the product.

Lee R.F.O. Plugs are available in aluminum and can be found in standard diameters ranging from 0.156 to 0.875 of an inch.

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Lee QIP® (Quick Installation Plug) Plugs

The Lee QIP was developed to provide an easier method of handling and installing the smallest plug sizes. This is accomplished by pre-installing the pin into the plug. This pre-assembled component adapts more easily to automated installation. Despite their smaller size, these plugs experience no loss of strength, with proof pressures up to 12,000 psi.

The Lee QIP is available in aluminum and is offered in four standard sizes: 0.093, 0.125, 0.156, and 0.187 inch diameters.

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Lee A.F.O.® (Axial Force Only) Plugs

Unlike other plugs in our product family, A.F.O. Plugs are both removable and reusable due to their threaded design, which allows technicians easy access to sealed passageways. In spite of this, the A.F.O. Plug still seals up to 56,000 psi. Each plug features a floating seal that self-aligns, allowing for threaded holes that aren’t concentric with the through-hole. Lastly, the A.F.O. designation means that no radial force is applied during installation, making this component suitable for thinner-walled housings. See Installation Process Specification P1013 (which applies to all A.F.O. Plugs) for more information.

A.F.O. Plugs are made from stainless steel and are available in standard diameters from 0.190 to 0.625 of an inch.

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Lee Dual Sealing A.F.O.® Plugs

The Dual Sealing A.F.O. Plug comes with all the strength and ease of use offered by our regular A.F.O. Plugs, but with added safety features for use in hydraulic systems. The incorporation of an O-ring allows users to vent gas out of a side port or safely release trapped high-pressure gas. This allows the Dual Sealing A.F.O. Plug to be used for “fill and drain” applications. In addition, a newer higher pressure version of this product is available with backup rings rated to seal up to 15,000 psi when partially open.

The Dual Sealing A.F.O. Plug is available in stainless steel and can be purchased in diameters of 0.3125, 0.375, 0.500, and 0.750 of an inch.

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Lee Cross Port Plugs

Lee Cross Port Plugs are a plugging solution specifically engineered to seal cross port passageways. This configuration is a variant of the original Lee Plug® that set industry standards over 65 years ago. A smooth wall design combined with the field-proven controlled expansion principle creates a permanent, leak-proof seal, without the need for O-rings or sealants. Installation is simple and reliable, and the plug requires no maintenance thereafter.

Lee Cross Port Plugs are ideal for isolating sections of a fluidic manifold. They are also used to plug deep passageways that are difficult to access with conventional sealing methods.

Lee Cross Port Plugs are constructed from 6Al-4V Titanium. They have been qualified for proof pressures over 20,000 psi and at temperatures up to 400°F. Configurations are available in 0.250, 0.281, and 0.343 inch diameters.

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Looking for a plug? Use the Product Finder to guide you to configurations that meet your requirements and gain access to detailed product information such as dimensions, performance specifications, CAD models, and more!

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Support & Resources

Support & Resources from a Team that Speaks Your Language

Partner with The Lee Company and get much more than just a supplier of top-quality fluid control products. Our reliable technical support team is available every step of the way to help you find solutions, maximize productivity, and drive efficiency across your operations. Check out these aerospace and defense-specific resources to learn more.

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Product Handbook
Technical Hydraulic Handbook of Aerospace, Energy, and Motorsport Solutions
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Technical Guide
PS 203 REV L: Design Criteria and Installation and Extraction Procedures for Lee Plug Expansion Plugs
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Technical Guide
PS 1013 H: Installation Procedures for A.F.O® Plugs
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Article
Dual Sealing A.F.O.® Plugs Provide Pre-Charge and Purge Functions
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Application Card
Fly With our Experience on Commercial Aircraft
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Product Video
Lee Plug Expansion Plug Features & Benefits Overview
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