Page 11 - Threading_Handbook

Handedness
This represents the direction of the thread helix, which can twist in two possible directions:
clockwise (CW) and counter-clockwise (CCW). When the thread is designed to be turned
in a clockwise direction, it is known as a “right-handed (RH) thread.” When the thread is
designed to be turned in the opposite direction, it is known as a “left-handed (LH) thread.” INTRODUCTION

View direction
Left hand Right hand

When turns CW, When turns CW,
screw-out plate screw-in plate

Pitch
Thread pitch can be classified by “coarse pitch” and “fine pitch.” The terms refer to the size
of the threads relative to the screw diameter and do not imply differences in thread quality,
tolerances, or cost. They can be compared as follows:

Coarse Pitch
• Fewer threads per axial distance
• Larger thread form relative to screw diameter
• More resistant to stripping and cross threading due to greater flank engagement

• Install much faster as they require fewer turns per unit length

Fine Pitch
• More threads per axial distance
• Smaller thread form relative to screw diameter
• Stronger due to a larger stress area for the same diameter thread

• Less likely to vibrate loose as they have a smaller helix angle and allow finer adjustment
• Develop greater preload with less tightening torque

Coarse Thread fine
thread length thread

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