In the realm of mechanical maintenance and repair, ensuring that components are properly lubricated is critical for longevity and performance. One indispensable tool in this process is the grease fitting, also known as a grease zerk.
These small but vital parts play a significant role in maintaining machinery by facilitating the application of lubricants directly to moving parts. If you have any questions about the content in this article, feel free to contact us for further assistance.
What Is a Grease Fitting?
Grease fittings, commonly known as grease zerks, are small but essential components used in a variety of mechanical systems to allow for the easy injection of lubricants (usually grease) into the system. Grease fittings ensure that moving parts, such as bearings, joints, and gears, stay lubricated, minimizing friction and extending the lifespan of the machinery.
Their importance in automotive, construction, and industrial equipment cannot be overstated, as they help reduce wear and tear, prevent overheating, and improve performance.
Grease fittings are found on machinery that requires regular maintenance for optimal performance. These small metal parts are typically installed in the component’s grease port, offering a simple method for applying grease using a grease gun.
When the grease is pumped through the fitting, it disperses into the moving parts of the machinery, providing lubrication and protection.
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Types of Grease Fittings
There are several types of grease fittings, each designed for different applications, sizes, and environments. The most common types include:
1. Standard Grease Fittings (Zerk Fittings)

These are the traditional grease fittings, often used in automotive and industrial machinery. They come in various sizes, including metric grease fittings and imperial grease fittings, allowing flexibility across different types of equipment.
2. Button Head Grease Fittings
Button head fittings are ideal for low-clearance applications. Their rounded, low-profile design allows for easy access in tight spaces.
3. Flush Type Grease Fittings
These fittings are designed for systems that require frequent cleaning. They offer a flush surface when not in use, helping to prevent contamination and maintaining cleanliness.
4. Right-Angle Grease Fittings
These fittings are used where a straight-fitting would not be easily accessible. They are ideal for tight, hard-to-reach areas where a 90-degree angle is required.
5. Needle Fittings
Needle fittings are used for precise, targeted grease application, often in very small parts or where only a small amount of grease is needed.
How Do Grease Fittings Work?
Grease fittings work by providing a designated port for grease to be injected into the mechanical parts of machinery. When you use a grease gun, the nozzle of the gun fits onto the grease fitting, and pressure is applied to push the grease through the fitting into the machinery.
The grease then lubricates the moving parts, such as bearings, joints, or shafts, reducing friction and preventing wear.
Standard Grease Fitting Sizes
Grease fittings come in different sizes, and it’s crucial to match the correct size to the grease port on the machine. The two primary standards for sizing are metric grease fittings and imperial grease fittings.
Metric vs Imperial Sizes
The difference between metric and imperial (or standard) sizes lies in their unit of measurement. Metric sizes are measured in millimeters, while imperial sizes are measured in fractions of an inch.
When selecting the appropriate grease fitting, it’s important to know whether your equipment uses metric or imperial dimensions.
Grease Zerk Size Chart

Here is a brief overview of common grease zerk sizes:
Size | Thread Type | Dimensions |
1/4-28 | Zerk Fitting | 0.250” (6mm) Thread |
M6 | Metric Zerk Fitting | 6mm Thread |
1/8-27 | Standard Zerk Fitting | 1/8” Thread |
3/8-24 | Zerk Fitting | 0.375” (9.5mm) Thread |
5/16-28 | Standard Zerk Fitting | 0.3125” (8mm) Thread |
These sizes are essential to consider when replacing or installing grease fittings.
Factors to Consider When Choosing Grease Fitting Sizes
When selecting a grease fitting, several factors need to be considered to ensure proper fit and function:
Equipment Requirements
Each machine or mechanical system has specific grease fitting requirements based on its design and the grease port size. Be sure to check the equipment manual for the correct size.
Operational Environment
The environment in which the equipment operates affects the choice of grease fitting. Harsh conditions, such as exposure to extreme temperatures, dirt, or moisture, may require specialized high-pressure grease zerks or fittings with additional sealing properties.
Type of Grease Used
The viscosity and type of grease used in the application can impact the choice of grease fitting. For example, heavy-duty grease may require a larger fitting to accommodate its thicker consistency.
Measuring and Identifying Grease Fitting Sizes
Tools and Techniques for Accurate Measurement
To accurately measure grease fittings, you will need a caliper or grease fitting gauge to measure the thread size and length of the fitting. The measurements are critical for ensuring that you choose the right replacement fitting.
Step 1: Measure the Thread Diameter
Using a caliper, measure the diameter of the grease fitting thread. This will help you determine the correct size of the fitting.

Step 2: Measure the Thread Pitch
Measure the distance between thread peaks using a thread gauge to determine whether it’s a fine or coarse thread.
Step 3: Verify Thread Compatibility
Check the fitting against your equipment’s specifications to ensure the thread type (imperial or metric) matches.
Selecting the Right Grease Fitting for Your Needs
Step 1: Determine the Equipment Compatibility
Check your equipment’s grease port specifications to identify whether you need a metric grease fitting or a standard grease fitting.
Step 2: Select the Correct Thread Size
Choose the thread size from the grease fitting chart to match your equipment.
Step 3: Evaluate Pressure Requirements
Consider the operating pressure of the equipment. Some fittings are designed for high-pressure environments, while others may be for low-pressure applications.
Step 4: Common Mistakes to Avoid
Avoid selecting the wrong size fitting, which can lead to poor lubrication, grease leakage, or damage to equipment.
Conclusion
Grease fittings play a vital role in the longevity and efficiency of machinery by ensuring proper lubrication. Selecting the right grease fitting sizes, understanding the different grease zerk dimensions, and considering the operational environment are crucial for successful maintenance. Always ensure compatibility with your equipment to avoid costly mistakes.
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FAQs About What is a Grease Fitting
What is a grease fitting used for?
Grease fittings are used to inject lubricant into various mechanical parts to reduce friction and wear. They are essential for maintaining machinery, such as bearings, joints, and gears.
How do I know what size grease fitting I need?
To determine the correct size, measure the diameter and pitch of the thread. Use a grease fitting gauge or calipers, and consult a grease fitting size chart for standard dimensions.
Can I use different types of grease fittings on the same equipment?
No, you should use the specific type and size of grease fitting recommended for your equipment. Mixing different fittings can lead to improper lubrication and equipment failure.
What is a grease zerk?
A grease zerk is a type of grease fitting that allows grease to be injected into a machine’s lubrication system. The term “zerk” often refers to the brand of fittings that became a standard term.
What happens if I use the wrong size grease fitting?
Using the wrong size can result in grease leakage, poor lubrication, or even damage to the grease port, leading to potential equipment failure.
Can I replace grease fittings myself?
Yes, replacing grease fittings is a relatively simple task. Ensure you select the correct size and type of fitting, and use a tool to properly install it.