Retaining rings are exceptionally useful fasteners that are mounted directly onto shafts to create a shoulder to retain an assembly. While past methods of securing shafts or housings required various machining operations, like drilling and tapping, and traditional fasteners like nuts, bolts, and cotter pins, retaining rings can simply be placed onto a recess on a shaft or housing to secure it. Retaining rings have 3 main benefits over traditional fastening methods for shafts and housings. Those benefits are listed below:
- Retaining rings help reduce assembly times since installation is simple and quick.
- Retaining rings reduce overall part weight and size since they are lightweight and have a small profile.
- Retaining rings help lower the total cost of raw material and labor needed to produce parts.
Because of these benefits, retaining ring use has become more common in various applications – from bearing retention to use in automobiles and exercise equipment. When purchasing retaining rings, however, there are some important things to consider – namely, expected loads on the ring, environmental conditions, and rotational speeds on the shaft, among others.
What Are Retaining Rings?
Retaining rings, also known as snap rings, are small, lightweight metal fasteners that either fix components onto a shaft or fix shafts into housings or bores. This is possible because retaining rings have a free end that allows the ring to be expanded (for installation on shafts) or compressed (for installation on housings) to be installed. Using a set of retaining ring pliers, retaining rings can easily be installed into a pre-cut groove on a shaft or a groove in a bore. Some retaining rings have lugs that allow them to be gripped by retaining ring pliers, while others do not. Once retaining rings are installed, they spring back to their original shape and grip the shaft or housing to create a tight hold. Additionally once installed, they form a shoulder on part assemblies that prevent components from deviating from their intended positions in the axial direction.
Retaining rings come in several different sizes to accommodate different size shafts and housings. Retaining rings are typically made from carbon steel, stainless steel, or beryllium copper alloys and can be subject to various finishing processes to accommodate different environments and loading. Our offerings for retaining rings are mostly made from stainless steel.
General Types of Retaining Rings
Internal vs. External Retaining Rings
In general, there are two main types of retaining rings – internal retaining rings and external retaining rings. Internal retaining rings are placed into a groove in a housing. Often internal retaining rings are tapered from the top of the ring to the free end of the ring. This is to help with installation since the overall height of the ring decreases as it is compressed. As a result, the ring can easily be inserted into the housing and can spring back to a circular shape once installed. This enables the ring to grip the entire groove in the housing and hence withstand higher thrust loads.
External retaining rings, unlike internal ones, are placed on a groove directly on the shaft. Using a set of retaining ring pliers, external retaining rings are expanded and then spring back to their original shape when installed to form a tight hold. A portion of the ring protrudes out the groove and forms a shoulder to prevent components on a shaft from shifting.
Axially vs. Radially Installed Retaining Rings
Retaining rings can either be installed axially or radially. Axial installation means retaining rings are installed from the end of the shaft and slid along the shaft’s axis until it is placed in the necessary groove. Radial installation means retaining rings are installed from a direction perpendicular to the axis of the shaft. One major advantage of axially-installed retaining rings is that they contact the entire surface of the groove it is placed in. This allows axially-installed rings to transmit thrust loads throughout the entire groove wall – making these rings able to sustain high thrust loads.
Despite their name, radially-installed retaining rings actually resemble a half-circle and are sometimes called E-clips. This is because there are three prongs on the inside of the ring that contact the groove. Radially-installed retaining rings do not have lugs that allow them to be gripped by a set of retaining ring pliers. Additionally, because of their half-circle shape, these rings do cover the entire circumference of the groove and hence cannot sustain high thrust loads as effectively as their axially-installed counterparts. Despite that, two major advantages of radially-installed retaining rings are that they are easier to install than axially-installed rings and are more cost-effective than other fastening methods, including their axial counterparts.
Important Design Considerations for Retaining Rings
1. Thrust Load
Retaining rings are often used in heavy machinery to secure shafts and their components in industries like automobile and aerospace where they are used in engine and bearing assemblies. Unsurprisingly, thrust loads, or loads that are applied along the axis of a shaft, can be exceptionally high in these applications, especially when power transmission is involved. Thrust loads are one of three that result from the rotational meshing of gears in power transmission. During meshing, a reaction force normal to the contact area between the teeth of the gears develops. This resultant normal force can be broken down into two vector components: the axial (coming out the gear) and radial directions (towards the center of the gear). As gears rotate, the axial and radial forces will oscillate. Therefore, it’s critical that the retaining rings you purchase are rated to handle the maximum expected loads in your project. Calculate both the axial and radial forces in your project and pick an appropriate retaining ring.
2. Centrifugal Force
Additionally, rotational speeds in power transmission applications can be exceptionally fast. Rapid rotational speeds can cause centrifugal forces to lift a retaining ring out of position. This is because as objects revolve around an axis, a reaction force pointed away from the rotational center develops. The faster the rotational speed, the higher the centrifugal forces. Therefore, it’s important to consider both expected loads and rotational speeds when purchasing retaining rings for your project as the type of ring that is used can have a tremendous impact on your project’s success.
Selecting a Retaining Ring
A quick note on part numbers: Although we mostly stock stainless steel retaining rings and add the respective shaft diameter per part, you can get a quick idea of clip specifications by looking at the part number code. Rotor Clip codes are abbreviated in the form Type, Size, Material, Finish. For example: SH-21ST PA refers to Shaft (SH), Nominal Shaft Diameter of 7/32” (21 / 100 = .21, or 7/32”), Carbon Spring Steel (ST), with a black phosphate finish (PA).
To help you find the correct ring from our selection, reference the chart below to determine which ring type suits your application:
|Radial||External||E||“E” – type||For shafts .040 – 1.375 ” in diameter|
|Radial||External||SE||“E” – type||Smaller free diameter than standard E rings|
|Radial||External||YE||“E” – type||Thicker than standard E rings|
|Radial||External||BSE||“E” – type||Bowed rings apply a spring force on parts; useful for taking up extra play|
|Note: For a full list of codes please review RCU The Ultimate Retaining Ring Guide p. 41|
Need to replace a broken retaining ring?
Combined with an understanding of how part codes work, use whatever information you have available with your measurements. Depending on the ring installation type, there are some common dimensions to measure to find your part.
- First measure the inside diameter of the housing (Housing-Dh) for internal applications or the outside diameter of the shaft (Shaft-Ds) for external applications.
- Take any available measurements of thickness (T), lug height (H), maximum section (S max), and minimum section (S min). Match your dimensions to the appropriate spec sheet below:
- Measure the outside diameter (G) and thickness (T) and match it to dimensions on the appropriate spec sheet:
|Note: For full instructions please review RCU The Ultimate Retaining Ring Guide p. 57|
Retaining rings are immensely useful fasteners for shafts and housings that do away with many of the troublesome headaches traditional fastening methods come with. The low-profile and lightweight retaining rings help reduce overall product assembly weights and footprints. Additionally, the easy installation of retaining rings means additional machining processes, like drilling and tapping, are no longer required. This helps reduce overall costs associated with both labor and hardware.
At Albany County Fasteners, we know a thing or two about fastening. Contact a sales representative today to discuss which retaining ring is right for your project.