How do you know what size grease fitting you have?

To determine the size of a grease fitting, you can measure the diameter of the fitting's threaded portion, typically using calipers or a micrometer. Common sizes include 1/8-inch NPT, 1/4-inch NPT, and others. Additionally, you can reference the manufacturer’s specifications for the equipment you're working on or consult a grease fitting size chart. If available, using a thread gauge can also help identify the fitting size accurately.