Loaded U-Cups Overview

Loaded U-Cups Seals, commonly referred to as “PolyPaks” or “Style 850” seals, are used in hydraulic applications. U-Cups are “loaded” with an o-ring placed within the groove. The o-ring acts as an energizer while in low-pressure conditions and increases seal performance in higher pressure rod and piston systems. The most common material is polyurethane, though alternatives may be provided upon request.

If you require more information or would like to request a quote on Loaded U-Cups, please give us a call at 832-224-2719 or fill out the Product Inquiry Form.

Loaded U-Cup Dimensions

Looking at the curvature throughout the u-cup, it can be difficult knowing where to start and end when measuring the dimensions. To eliminate confusion, Cross-Section is defined by the width at the bottom of the u-cup. Inside Diameter and Outside Diameter are also measured from the bottom of the u-cup. See the diagram below:


Seal Information
Material (U-Cup) 95A TPU
Material (Energizer) 70A NBR
Temperature Range -31° – +212° F
Pressure Range 0 – 5,000 PSI
Speed 3 FT/SEC





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Loaded U-Cup Part Numbering System

Part numbering follows a specific order: Loaded ring, Cross-Section (in.), Inside Diameter (in.), Height (in.), and optional lip beveling. The left example shows a u-cup that is loaded with an o-ring energizer, has a cross-section of .125 inches, an ID of 1 inch, a height of .250 inches, and is made with a bevel lip. This is a Deep Style. The right example shows a u-cup that is loaded with an o-ring energizer, has a cross-section and height of .250 inches, an ID of 1 inch, and is made with a bevel lip. This is a Square Style.

Deep Style Loaded U-Cup

Square Style Loaded U-Cup

Loaded U-Cup Profiles

Loaded U-Cups come in the following styles:

Straight Lip Bevel Lip

Common Cross-Section Sizes

The following are the most common cross-section sizes:

Cross-Section Fractional
0.125 1/8″
0.188 3/16″
0.250 1/4″
0.313 5/16″
0.375 3/8″
0.500 1/2″
0.625 5/8″
0.750 3/4″
1.000 1″


Loaded U-Cup Size Chart

In the table below, you will find the most common Imperial sizes.

Note: Loaded U-Cups can be made in virtually any size (inch or metric dimensions), so if the size you need is not listed here, submit the Product Inquiry form or contact us

Size CS ID OD H CS (Fractional) ID (Fractional) OD (Fractional) H (Fractional)