To measure thread size with a tape measure, you typically focus on two key dimensions: the length and the diameter of the threaded portion. While a tape measure is excellent for length, accurately measuring the small diameter of threads can be challenging compared to tools like calipers, but it's possible for a rough estimate.
Here's how you can measure using a tape measure based on common practices and the provided information:
Measuring the Length of the Thread
The length of a thread is usually measured from the point where the thread begins under the head of the fastener to the end of the threaded part.
- Step 1: Place the end of the tape measure against the bottom of the fastener's head.
- Step 2: Extend the tape measure down the threaded portion.
- Step 3: Read the measurement at the very end of the threaded area.
Reference Information: Measure from the bottom of the head to the end of the threaded area in millimeters. For instance, it might be 8 millimeters.
This length is a crucial part of identifying the thread size.
Measuring the Diameter of the Thread
The diameter is the width of the threaded shaft. Measuring this accurately with a flexible tape measure is less precise than with rigid tools, but you can get an approximate measurement.
- Step 1: Wrap the tape measure around the threaded shaft.
- Step 2: Note the circumference measurement (the distance around the shaft).
- Step 3: Divide the circumference by Pi (approximately 3.14159) to get the diameter.
- Alternative (Less Accurate): For a very rough estimate, you might try to hold the tape measure across the widest part of the threads, being careful to measure the distance from one side to the other across the center. This is very difficult with a flexible tape measure.
Reference Information: Then, measure the diameter (width) of the threaded area in millimeters. This might be 4 millimeters across.
Practical Example
Let's apply the reference examples:
- Length Measurement: You measure from the bottom of the head to the end of the threads and get 8 millimeters.
- Diameter Measurement: You measure the width across the threads and find it is approximately 4 millimeters.
Based on these two measurements – length and diameter – you can begin to identify the thread size. Standard thread sizes are often described by their major diameter followed by their length (e.g., M4x8 mm).
Understanding the Measurements
Here's a simple breakdown:
| Measurement | What it Measures | How to Use Tape Measure (Approx.) | Example (from reference) |
|---|---|---|---|
| Length | From under head to end of thread | Align tape end under head, measure to thread end. | 8 mm |
| Diameter | Width across threads (major diameter) | Wrap tape for circumference, or attempt to measure width across center. | 4 mm |
Using these two measurements together gives you the basic dimensions needed to identify or specify a thread size, although additional information like thread pitch (distance between threads) is needed for complete identification, which cannot be measured with a standard tape measure.
