There are a wide variety of grease fitting sizes and styles available to choose from, but determining the correct size for your needs can be boiled down to just critical 3 dimensions. A basic understanding of the ‘anatomy’ of a grease fitting will turn a grease fitting novice into an expert in no time.
NOTE: The figure below is used for reference and show ¼”-28 Taper Thread Grease Fittings in straight, 45°, and 90° orientation, which represents the most common type, and for all intents and purposes, the foundation of all other grease fitting styles.
Dimension B is the “Thread Length” and measures the depth of female threaded area that has been created for the male threads in the base of the grease fitting.
- This is most important of all grease fitting specifications because it fastens and thus completes the seal between the fitting and the component into which it is threaded.
- The Thread Length can be imperial or metric.
- Thread types can be either domestic (SAE) or Metric (DIN).
- Use a female thread gauge to determine the Thread Length in situations where the original grease fitting specification is unknown or missing.
Dimension A is called the “Overall Height” and measures (you guessed it) the overall height of the fitting from bottom to top when standing flush against a flat, horizontal surface (when uninstalled).
- Overall Height must be such that the fitting will fit into the space allotted when it sits flush against the component into which it is threaded.
- NOTE: if you haven’t noticed already, grease fittings tend to be crammed into tight spaces, making this one of the most critical dimensions of the grease fitting.
Dimension X is called the “Hex” because it has six sides.
- The primary role of the Hex is for installation, where it sits flush against the component into which it is threaded.
- When installing a grease fitting, you will need a wrench, socket, or grease fitting installation tool that matches the size of the Hex dimension.
- The Hex size can be either imperial or metric.
- Because the Hex is primarily for installation it does not require as many size variations and standard Hex sizes will easily match wrench or socket head sizes.
Fitting Angle is not necessarily assigned a dimension, but is another primary specification for determining the correct grease fitting size for your application.
- The three most common grease fitting angles are straight, 45°, and 90°, but others are in-stock and available from SAE Products.
- Angle orientation selection is dictated by the amount of space allocated for the grease fitting as well as optimization for lubrication access and maintenance.
Instructions for determining the size of a replacement grease fitting:
- Measure Hex size (dimension X) and uninstall the grease fitting using the appropriately sized wrench, socket, or grease fitting tool.
- Measure the Thread Length (dimension B)
- Measure the Overall Height (dimension A)
- Note the angle orientation
Instructions for determining the correct grease fitting size for a new grease fitting install:
- Use a female thread gauge to determine the Thread Length (dimension B) required
- Measure the amount of space allocated for grease fitting height once installed and combine with dimension B to determine Overall Height (dimension A)
- Determine the ideal angle orientation to meet height requirements as well as access for lubrication and maintenance tools.
- Use a wrench to install the grease fitting that matches the Hex (dimension X).
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