Machine Design
Gear box is used

To produce torque
To obtain variable speeds
To increase efficiency of system
For speed reduction

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Machine Design
A bolt of M 24 × 2 means that

The effective diameter of bolt is 24 mm and there are 2 threads per cm
Cross-sectional area of the threads is 24 mm²
The pitch of the thread is 24 mm and depth is 2 mm
The nominal diameter of bolt is 24 mm and pitch is 2 mm

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