A thread gauge works by acting as a precise physical standard to check the dimensions of screw threads. It verifies whether the thread's angle, pitch, and diameter are within specified tolerances.
Understanding Thread Gauges
Thread gauges are crucial for quality control in manufacturing, ensuring that threaded parts will fit together correctly. The reference specifies that thread gauges come in two main types: plug gauges for internal threads and ring gauges for external threads. Each type includes a "GO" gauge and a "NO GO" gauge.
How Thread Gauges Function
The function of a thread gauge can be broken down into the following steps:
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Identify the Thread Type: Ensure the gauge matches the thread form (e.g., metric, unified) and size being tested.
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Prepare the Threaded Part: Clean the threaded component to remove any debris that might affect the gauging process.
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"GO" Gauge Test:
- The "GO" gauge should easily screw into (internal thread) or onto (external thread) the part's threads with minimal force.
- This indicates that the thread is not undersized and is within the lower tolerance limit.
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"NO GO" Gauge Test:
- The "NO GO" gauge should not fully engage with the threads. It should only enter a few turns at most.
- If the "NO GO" gauge enters too far, it suggests the thread is oversized or has an incorrect pitch, exceeding the upper tolerance limit.
Types of Thread Gauges
| Gauge Type | Used For | Function |
|---|---|---|
| Plug Gauge | Internal Threads | Checks if internal threads are within specified dimensions. |
| Ring Gauge | External Threads | Checks if external threads are within specified dimensions. |
Interpretation of Results
- Pass: If the "GO" gauge passes and the "NO GO" gauge does not, the thread is within acceptable limits.
- Fail: If either the "GO" gauge does not pass or the "NO GO" gauge does, the thread is outside of tolerance and considered defective.
Example
Imagine you're checking an internal thread using a plug gauge.
- You select the correct plug gauge size and thread type.
- The "GO" plug gauge screws in smoothly.
- The "NO GO" plug gauge only enters a couple of turns.
The threaded part passes the test and is deemed acceptable.
