To measure a grease fitting, you use specific tools to determine its size and type.
Measuring grease fittings is essential for identifying the correct replacement or understanding the specifications of a fitting. The process involves two primary measurements using specific tools.
According to the provided reference, to measure a grease fitting, use a caliper to measure the thread diameter and a thread gauge to determine the thread pitch. This process helps you identify the correct size and type, whether metric or imperial.
Steps for Accurate Measurement
Here's a breakdown of the process:
- Gather Your Tools: You will need a caliper (preferably a digital or vernier caliper) and a thread gauge (either a screw pitch gauge or a dedicated thread gauge set).
- Clean the Fitting: Ensure the fitting's threads are clean and free of grease or debris to get an accurate measurement.
- Measure the Thread Diameter:
- Use the caliper to measure the outside diameter of the threads.
- Place the caliper jaws across the widest part of the threads.
- Note the reading. This measurement is crucial for determining the base size (e.g., 1/8 inch, 1/4 inch, M6, M10).
- Measure the Thread Pitch:
- Select leaves from the thread gauge set.
- Find the leaf that perfectly fits into the thread grooves without any gap or wobble.
- The number on the leaf indicates the pitch. For imperial threads, this is usually the number of threads per inch (TPI). For metric threads, this is the distance between two adjacent thread crests in millimeters (mm).
- Identify Type and Size:
- Compare your diameter and pitch measurements against standard grease fitting charts.
- The combination of diameter and pitch will tell you the exact size and whether it's a metric (e.g., M6x1, M10x1.5) or imperial (e.g., 1/8"-27 NPT, 1/4"-28 SAE-LT) fitting.
Why Accurate Measurement Matters
Knowing the precise thread diameter and thread pitch is critical because grease fittings come in various sizes and thread types (metric and imperial being the most common). Using the wrong size or thread type can lead to:
- Difficulty threading the fitting.
- Damage to the port or the new fitting.
- Leaking grease, which defeats the purpose of lubrication.
Common Grease Fitting Thread Types
Understanding the nomenclature helps when matching measurements:
- NPT (National Pipe Taper): Common imperial pipe thread, often found on fittings. Tapered threads seal by interference.
- SAE-LT (Society of Automotive Engineers - Lubrication Type): Imperial straight thread, often used with a sealing surface on the fitting nose.
- Metric: Straight threads measured in millimeters (e.g., M6, M8, M10) followed by the pitch in millimeters (e.g., M6x1, M10x1.5).
By accurately measuring both the diameter and pitch, you can ensure you select the correct fitting for your application.
