How to Use Hexagon Socket Set Screws 

If the Set Screw Size Cannot Be Increased

Note that even if two set screws are used for applications that require a great shaft holding power, the shaft holding power is not necessarily doubled. The reason is that the shaft holding power varies depending on the opening angle between the two set screws. The following figure shows this relationship.

Opening Angle of the Set Screw and
   Shaft Holding Power

Hardness and Shaft Holding Power

The greater the tightened shaft hardness, the lower the shaft holding power. The following figure shows this relationship.

Set Screw and Shaft Hardness and
   Shaft Holding Power

Set Screws and Fit Length

With an increasing use of materials such as zinc die-cast and ironbased sintered alloy in the female screw parts, the allowable load of the female screws decrease resulting in problems. This problem can be solved by increasing the thickness of the female screw part. The following figure shows the relationship between the fit length of the set screw and the strength of the female screw material.

Female screw strength and fit length of
   set screw

Parallel Misalignment Amount of Female Screw Hole

If the female screw hole is displaced from the center of the tightened shaft, the shaft holding power decreases. The following figure shows this relationship obtained from an experiment with the M4 set screw.

Parallel Misalignment Amount and
   Shaft Holding Power of Female Screw

Shaft and Hub or Flange Hole Fit Accuracy

The shaft holding power does not decrease very much until the shaft accuracy h9 for the hole standard as shown in the figure below. Since the fit accuracy is expected to have considerable influence in a dynamic operating environment, sufficient attention needs to be paid to the fit accuracy.

Fit Accuracy of the Bushing Hole and
   Shaft Holding Power