Dimension
The dimension describes the geometric specifications of a tool or component – e.g. length, diameter or thread depth. When tapping threads, precise dimensions are crucial:
- Only correctly sized tools guarantee a clean and accurate thread.
- Deviations can lead to assembly problems or damage.
Practical example: An M8 tap (metric ISO thread, coarse thread) requires a core hole with the correct diameter (e.g. approximately 6.8 mm). If the dimension is incorrect, the screw will not be able to be threaded in later.
Calculation – The rule of thumb is:
Core hole diameter ≈ nominal diameter – pitch
- For M8 × 1.25 (coarse thread):
8.0 mm – 1.25 mm = 6.75 mm → rounded to 6.8 mm - For M8 × 1.0 (fine thread):
8.0 mm – 1.0 mm = 7.0 mm - For M8 × 0.75 (fine thread, less common):
8.0 mm – 0.75 mm = 7.25 mm