A snap ring is a strong, thin, C-shaped metallic ring that works as a retaining fastener for assembly parts on shafts and inside circular bores. Unlike a nut or bolt that threads onto a piece, a snap ring or C-clip snaps into a circular groove inside a bore housing or on the shaft. That is why it is called a snap ring because it has high tensile strength that makes it snap into the radial groove and stay in place.
Once the snap ring sits properly in the groove, part of its circumference sticks out to form a shoulder that secures the assemblies inside the housing or onto the shaft. This is why they are called retaining rings because they retain components in an assembly.
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How a snap ring works
To understand a snap ring even better, let’s take a look at how it works. A snap ring or retaining ring has a C-shape or circular shape with a gap. The gap allows the ring to expand or compress.
When installing a snap ring inside a bore or housing, you pull the ends of the ring together to compress it and release it into the groove. You can do this by hand or use a special snap ring tool such as snap ring pliers.
On the other hand, when installing the ring on a shaft, you pull the ends apart, slide the ring on the shaft, and release it onto the circlip’s groove on the shaft.
Ideally, the size of the section of a circlip is larger than the depth of the groove to which it is installed. This ensures that a portion of the section of the C-clip remains exposed to act as a shoulder for retaining components or an assembly inside a housing or on the shaft.
Similar to other retaining clips, snap rings or circlips are made from very high tensile materials. Examples of such materials include carbon steel, vanadium chrome steel alloy, and beryllium copper. These materials are strong enough to withstand extreme pressure and heat. That is why snap rings used in the assembly of floating pistons hardly fail despite the intense movement of the conrod and the high levels of heat in the chamber.
Circlips are also not easy to deform when compressing or expanding them. However, that does not mean they are indestructible. If you handle the ring fasteners the wrong way or use the wrong tool, you can easily deform them and cause them to fail prematurely. Check out this article to learn some things that can cause snap rings to deform and how to avoid them.
Types of snap rings
There are many types of snap rings or retaining rings. They are classified broadly into 2 main categories: external snap rings and internal snap rings.
External snap rings are retaining rings that wrap around a shaft to retain shaft assemblies. They are used in many applications including retaining the bearings on axles and in gear assembly inside the transmission.
On the other hand, internal snap rings are retaining rings that are installed inside a bore or housing to keep assemblies or components from coming out. An example of their application is in the installation of a piston pin or gudgeon pin in the floating piston assembly. The circlip on the piston retains the piston pin or wrist pin in place while allowing it to rotate freely in both the piston and connecting rod.
Circlips are also classified according to their design. The following is a list of their classification based on design:
- Tapered section snap ring
- Constant section snap ring
- Spiral lock snap ring – you can have single-turn or multi-turn spiral rings
- Circlip with grip holes
- Circlip without grip holes
Differences between external and internal snap rings
| External circlip | Internal circlip |
|---|---|
| Installed outside on a shaft | Installed inside in a bore |
| Expanded to install and remove | Compressed to install and remove |
| Makes contact on its internal circumference | Makes contact on its external circumference |
How to measure snap rings
Tools needed:
- Vernier calipers
Unlike hog rings, snap rings are a perfect circle. Thus, they are measured by their diameter. The ring fasteners come in different sizes, which is determined by the diameter of the shaft or bore where they will be installed.
External C-clips are measured by their internal diameter whereas internal C-clips are measured by their external diameter. However, manufacturers specify both internal and external diameters for both types of circlips.
Measuring internal snap ring
As I said, internal circlips make contact on their external circumference. So, to measure their size, you measure the external diameter. Here is how to do it with vernier calipers.
- Slide open the main jaws
- Place the snap ring between the jaws
- Close the calipers on the fastener until it is secure
- Tighten the screw clamp to ensure that the measurement does not change when reading the scale.
- Read the main scale and the vernier scale
In contrast, an external snap ring makes contact with a shaft on its internal circumference. So, you determine its size by measuring the internal diameter. Here is how to measure it with vernier calipers.
Measuring external snap ring
Because external snap rings contact the shaft with the internal circumference, you determine its size by measuring the internal diameter. This is how to do it with vernier calipers.
- Place the external circlip on a flat surface
- Close the smaller jaws (top jaws) of the vernier caliper
- Put the jaws inside the external circlip. The gap on the circlip should face away from you.
- Open the small jaws until they make contact with the internal circumference. Make sure you don’t apply tension on the c-clip.
- Tighten the screw clamp to keep the measurement from changing.
- Read the vernier caliper and record the measurements.
Another important dimension when measuring snap ring fasteners is the thickness of the ring. The measurement helps determine if the retaining clip will fit in the radial groove on the shaft or inside the bore housing. You can measure it anywhere on the ring.
Simply hold the ring upright and put it perpendicular between the main jaws. That is, the hollow part should face the jaws. Then close the jaws until they touch both sides of the ring. Now read the vernier scale and record the measurement. That is the thickness of the snap ring. Compare the measurement with the values in the repair manual of whatever you are fixing.
In case you do not know how to use vernier calipers, check out this video.
How to install snap rings or circlips
There is more than one way to install a snap ring fastener. You can install it with a tool or without. Installing a snap ring without a tool means sitting the ring fastener in its groove by hand.
On the other hand, installing snap rings with a tool means using either a flat screwdriver, a snap ring tool, or needle nose. pliers. In this section, I will cover in more detail all the three methods of installing circlips.
How to install snap rings/circlips without a tool or by hand
This is the most difficult method of installing a circlip. It is also very risky because the circlip can snap out of your hand into your eyes. Furthermore, installing a circlip by hand can also hurt your fingers. So, ensure you put on some safety glasses at least and a pair of leather gloves before attempting to install. Then follow these installation steps:
Installing internal snap ring
- Grab the snap ring.
- Insert one end of the circlip inside the retaining ring groove on the bore or housing. The rest of the circlip should be on the top surface of the bore.
- Press the other end of the circlip with your thumb while guiding it into the bore.
- At the same time, press the rounded side of the circlip with your other hand. This might hurt your fingers and that is why you need a pair of leather gloves. Place your hand in such a way that it prevents the circlip from snapping onto your face in case it snaps.
- Press until the entire snap ring fits around the circumference of the bore or housing.
- Now apply gentle vertical pressure relative to the bore to sit the ring into its groove. You can do this by applying pressure gently on different positions on the ring’s circumference. This will ensure that the ring does not twist and snap out.
Installing a circlip by hand can be easy or hard depending on the tensile strength of the ring. Very strong circlips are difficult to install by hand and can be a safety hazard for the installer.
Installing external snap ring
Installing an external snap ring is the opposite of the above method. Instead of compressing the ring, you expand it. Here is how to do it by hand.
- Hook one end of the C-clip onto the radial groove of the shaft.
- Pull the other end of the circlip to expand its internal diameter to fit the shaft.
- Once the ring is on the circumference of the shaft, push it gently inward into the groove.
- Inspect to ensure the snap ring is seated properly in the groove.
How to install snap rings with a screwdriver
A flathead screwdriver is one of the readily available tools for installing retaining clips. It is particularly ideal for circlips that do not have grip holes or notched ends. This is how to use it:
Installing internal circlip
- Insert one end of the circlip in the internal groove.
- Apply some pressure on the other end of the snap ring with your thumb.
- Use a flathead screwdriver to pry the middle of the snap ring. The pressure from your thumb at one end and the pressure from the screwdriver compresses the circlip to fit in the bore.
I find installing a circlip using a flat screwdriver more effective than with fingers.
Installing external circlip
To install a circlip on an external groove with a flat head screwdriver, follow these steps:
- Wear a pair of safety glasses.
- Hook one end of the circlip onto the groove on the shaft.
- Hold the other end between your fingers to keep the snap ring from spanning on you.
- Pry the circlip at the middle with the flathead screwdriver to expand the loop of the ring.
- Now slip the expanded snap ring into the groove of the shaft.
How to install snap rings/circlips with snap ring pliers or needle nose
A pair of snap ring pliers is a tool designed specifically to install or remove snap rings. There is external snap ring pliers for installing and removing external snap rings and internal snap ring pliers for internal circlips.
Using external snap ring pliers
This method applies to snap rings with grip holes or grooved tips. Unfortunately, you cannot use needle nose pliers to install external snap rings because they close the jaws when you squeeze the handles whereas external snap ring pliers open the jaws when you close the handles. Follow these steps
- Begin by putting on a pair of safety gloves to shield your eyes from accidental snapping out of the circlip.
- Insert the tips of the snap ring pliers or needle nose pliers into the grip holes or grooves of the circlip.
- Close the handles of the circlip pliers to open the tips. This widens the loop of the snap ring.
- Slide the expanded snap ring into the groove on the shaft.
Using internal snap ring pliers or needle nose pliers
Again, this method only applies to snap rings that have either grip holes, grooved ends, or bent ends. These are the steps to follow:
- Put on some safety goggles.
- Insert the tips of the internal snap ring pliers into the circlip grip holes or grooves.
- Press the handles of the pliers to pull together the ends of the circlip. This compresses the ring so that it can fit the bore or housing.
- Carefully slide the compressed snap ring into the internal wire lock groove and release it.
- Inspect to ensure the ring sits in the groove properly.
Frequently Asked Questions
You can always reuse a snap ring for as long as it is not deformed, corroded, or broken. Also, check to ensure that the old snap ring creates the required tension to stick in the radial groove without coming out.
A snap ring is a type of retaining ring. Other retaining rings include e-clips, spiral-wound rings, and stamped rings among others. They hold an assembly together.
A pair of snap ring pliers is the best for removing and installing snap ring fasteners with eyelets or hooks. You can also use needle nose pliers with sharp notched jaws, especially for retaining rings that do not have eyelets.
