What are Retaining Rings?
Retaining rings, also referred to as snap rings or circlips rings, are metal fasteners that are installed in a groove on a shaft or in a housing or bore, establishing a shoulder that retains an assembly.
The devices retain these parts with a compact and light-weight design, requiring fewer machining operations than typical fastening techniques.
Recent years have seen a trend shift away from fastening metals with threaded fasteners towards fastening with retaining rings.
Retaining rings eliminate the threading, tapping, drilling and other machining operations you would find with more traditional fasteners, such as screws, nuts, bolts, cotter pins, washers, and more.
You should be able to dramatically reduce your manufacturing costs as the grooves can be machined from other manufacturing processes. Overall, retaining rings provide a more compact, functional design than traditional forms of fastening metal together.
Engineers specify and use retaining rings with consideration to the application on the specific:
- Installation and removal requirements
- Rotational speed
- Conditions and operating environment
- Expected force load(s) on the ring
- Cost
Retaining rings can be from 1 mm to 1 m in diameter. The variations in size, material, shape, and form result in designs that are utilized for many different applications across many industries.
For example, a typical passenger vehicle will have 50+ retaining rings in the powertrain, steering, and passenger safety systems.
Retaining rings are also found in a myriad of applications across various industries. Some of these applications include fitness equipment, wind turbines, storage brackets, bicycles, doorknobs, gas pumps, office equipment, and many others.
Types of Retaining Rings
There are four main types of retaining rings available, each of which may then be broken down into sub-types depending on unique application needs:
- Tapered section
- Axially assembled
- Inverted
- Beveled
- Bowed
- Radially assembled
- Self-locking
- Axially assembled
- Constant section
- Spiral
- Circular push-on
1. Tapered section retaining rings
The tapered section retaining rings are attached symmetrically from the center towards the free ends which remain circular when they are contracted or expanded within the boundaries of normal usage. This means that the ring will contact the groove freely along the whole periphery of the ring.
These rings may be fitted axially (horizontally from the center point of an axis) or radially (outside the radius of a circle). Depending on the size of the ring in question can be shaped one of two ways.
- For smaller rings: die and stamping on a press from steel or copper coil.
- For larger rings: wire forming where rectangular wire is coiled into the shape of a ring.
1.1 Axially assembled
Retaining rings are axially assembled into machined grooves in housings/bores (internal) or on shafts (external). The rings are produced with lug holes, small holes in the lugs of both axial internal and external retaining rings, for use in installing/removing them, with pliers designed for retaining rings.
1.1.1 Inverted retaining rings
Inverted Retaining Rings are a type of axially assembled rings with the lug holes inverted so that they fit into the bottom of the groove.
Inverting the lugs provides more clearance on a shaft or in a housing, while also forming a higher uniform shoulder which is desirable for retaining bearings and other components with large corner radii or chamfers.
1.1.2 Beveled retaining rings
Beveled retaining rings have a 15° beveled or angled edge. The angle allows it to wedge itself between the groove and the retained part until it can no longer be wedged, effectively, “locking” everything in place.
Think of when you put a cork in a bottle. You push the cork towards the opening until it can be wedged as deep into the opening as it can be.
The same thing happens when the beveled retaining ring is installed into your application. The ring is wedging itself into place between the groove wall and the retained part. This phenomenon is what we refer to as rigid end-play take-up.
1.1.3 Bowed retaining rings
Bowed retaining rings are curved versions of flat internal and external retaining rings and apply a pre-load to an assembly when they are installed in the groove. The pre-load takes up the end-play and, like a spring holds the assembly compressed.
Because parts can not be manufactured to an exact dimension, if they are manufactured to the low side of the tolerance, then installed with a standard ring, they will be loose or have a play on the shaft.
If manufactured on the high side of the tolerance, then they will extend more into the groove and not allow a standard ring to be fully installed. Bowed retaining rings are designed to compensate for accumulated tolerances and will act as a spring once it is installed into the groove.
1.2 Radially assembled
Radially applied retaining rings are externally installed into a shaft with machined grooves. They have no lug holes, and with regards to installation, they can only be installed with applicators.
1.3 Self-locking
Self-locking retaining rings can be installed in a housing/bore or on a shaft that has no machined groove. Self-locking rings with no lug holes can only be removed by destroying the ring or distorting it beyond the specified tolerances.
2. Constant section retaining rings
Constant section retaining rings (or snap rings) are manufactured with a uniform, constant section. In other words, the ring material is the same width at any point along the circumference of the ring.
When subjected to contraction, or expansion, infinite elliptical deformation occurs. As a result, the have contact with the groove at three or more points of contact, but never around the entire periphery. These rings are issued from either flat, or round, wire.
3. Spiral retaining rings
Spiral retaining rings are installed axially within housings/bores (internal) or onto shafts (external), making 360° contact with the groove.
Spiral retaining rings do not have ears or lugs that would be obtrusive during assembly. They are manufactured by coiling flat wire into the shape of the finished retaining ring.
Spiral rings are provided with a removal notch to facilitate the removal of the ring. Spiral retaining rings can be economically made in special alloys such as stainless steel because there is no scrap for the manufacturing process.
No special tools are required to install or remove. Duck-billed pliers can be used to install and remove external spiral rings.
4. Circular push-on
A Round Push-on ring looks like a serrated washer, which is usually made of metal. They can be installed by pressing onto the end of a grooved shaft until the inner teeth of the nut snap into place in a groove. The use of push nuts can save the cost of threading a nut onto the end of the shaft when being manufactured.
Advantages of Retaining Rings
- Less shaft/housing preparation (threading, tapping, drilling, etc.)
- Reduced weight and size of finished design
- Lower costs of raw material and labor
- Cheaper compared to other fastening methods
- Use less raw material for a given size
- Reduce and avoid complex machining such as threads and undercuts
- Compact design and Can be assembly quicker
- No special training is required for assembly
- Lightweight and Easy to install
- Unlike threaded alternatives, significantly reduces production cost
FAQs
What is the purpose of a retaining ring?
Retaining rings are used to hold components onto a shaft or into a bore. The smooth, round finish of most shafts or bores makes them difficult to attach to with alternative methods, whereas retaining rings clamp around them and create a shoulder that keeps parts in place.
What does a retention ring do?
A retaining ring is a fastener that holds components or assemblies onto a shaft or in a housing/bore when installed – typically in a groove – for one time use only. Once installed, the exposed portion acts as a shoulder which retains the specific component or assembly.
What is the difference between circlip and retaining ring?
Retaining ring, snap ring, and circlip are terms often used interchangeably referring to the same part a retaining ring with spring like features that is used to retain a part on a shaft or inside a housing or bore.
What is the other name of retaining ring?
A retaining ring (often referred to as a circlip or snap ring) is a fastener that holds components or assemblies onto a shaft or in a housing/bore when installed. Circular push-on retaining rings may be installed in applications where there is no groove.
What are the two main types of 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.
Where do you put a retaining ring?
Retaining ring grooves are, more often than not, located toward the end of a shaft or bore. This is usually to accommodate the installation and removal of radially installed retaining rings. It is more important not to locate the groove too close to the end of the shaft to avoid the risk of shearing.