Reading a metric thread gauge involves determining the thread's diameter and pitch, typically expressed as "M" followed by the diameter in millimeters and then the pitch in millimeters.
Here's how to decipher a metric thread designation, using the example "M10 x 1.5":
- M: Indicates that the thread is a metric thread.
- 10: Represents the nominal or major diameter of the thread, which is 10 millimeters. This is the approximate outside diameter of the threaded bolt or screw.
- x 1.5: The "x" separates the diameter and pitch. "1.5" represents the thread pitch, meaning the distance between two adjacent thread crests is 1.5 millimeters.
So, "M10 x 1.5" specifies a metric thread with a 10 mm diameter and a 1.5 mm pitch.
Key Considerations:
- Coarse vs. Fine Threads: For a given diameter (like M10), different pitches exist. A standard or "coarse" pitch is most common. Finer pitches (like 0.75 or 1.0 for M10) are used in applications needing more holding power, resistance to loosening, or finer adjustments. If the pitch is not explicitly stated, it's typically assumed to be the standard coarse pitch.
- Thread Gauges and Measurement Tools: While the thread designation tells you the intended dimensions, physical thread gauges or thread pitch gauges are used to verify the thread's accuracy. These gauges have a series of leaves with different pitches; you find the leaf that fits snugly into the thread to determine the pitch. Calipers can measure the thread diameter.
Example Breakdown:
- M6 x 1: Metric thread, 6 mm diameter, 1 mm pitch.
- M8 x 1.25: Metric thread, 8 mm diameter, 1.25 mm pitch.
- M12 x 1.75: Metric thread, 12 mm diameter, 1.75 mm pitch.
