Question

Draw to scale 1:1, the standard profile of EXTERNAL METRIC THREAD taking enlarged pitch as 50 mm. Give standard dimensions.

Hint:

In metric threads, always maintain a 60° included angle and use the flat crest/root dimensions for standard representation.

Answer 1

A metric thread profile is defined by ISO standards and consists of symmetrical V-shaped threads.
The external metric thread (bolt) profile is drawn using a triangular form with specific proportions based on the pitch (P).
Given: Pitch = 50 mm (enlarged for clarity)
Standard profile dimensions for external thread:
- Included angle of thread = 60\degree
- Thread depth (H) = $0.866 \times P = 0.866 \times 50 = 43.3$ mm
- Flat at crest = $0.125 \times P = 6.25$ mm
- Flat at root = $0.25 \times P = 12.5$ mm
- Thread height (actual depth cut) = $\dfrac{5}{8} \times H = 27.06$ mm
Construction steps:
1. Draw a horizontal base line.
2. Mark the pitch distance (50 mm) for each thread repetition.
3. Draw a V-profile with 60° included angle between each crest and root.
4. Flatten the crest and root as per standard dimensions.
5. Repeat for 2–3 threads.
Label the drawing:
Title: Standard External Metric Thread (Enlarged Pitch = 50 mm)
Scale: 1:1