• Torque control - a torque wrench is used to measure the amount of tightening
• Angle control - the angle of the turn is measured after initial contact
• Gut instinct - the most common but least reliable method

Conventional spring lock washers have been shown to NOT be effective and can actually aid self loosening rather than prevent it.

Although many locking mechanisms are available some of the most common effective methods are:

• Serrated Flange Screw Head - An enlarged flange integral to the screw head has several ramped teeth that allow the bolt to rotate in the tightening direction but lock into the bearing surface when rotated in the loosening direction.
• Nylon Insert Nut - This non-metallic friction locking device has a plastic insert which provides a thread locking function.
• Chemical Locking - Adhesives prevent loostening by filling the gaps between the male and female threads and bonding them together. "Loctite" is a command brand. This method provides the greatest resistance to vibration loosening.

Fine threads are stronger.

Fine threads have less tendency to loosen.

Fine threads since the thread incline is smaller and hence so is the off torque.

Fine threads allow finer adjustments when used for that purpose.

Fine threads are easier to tap ini hard materials.

Fine threads allow for thin walled tubes.

Fine threads requires less torque for the same preload.

Fine theads are more susceptible to galling.

Fine threads need longer thread engagements.

Fine threads are more prone to damage and thread fouling.

Fine threads are less suitable for high speed assembly.

Fine threads in metric sizes are less readily available.

Forumulas are readily available to compute thread engagement. However, here are two tips for a quick guide in non-critical common applications where the material of the bolt and nut are similar.

One is the go by the depth of common nuts. Another rule of thumb is that going deeper than the thread diameter X 2.0 is a waste of tapping time as it does not add strength. In fact factors ranging from 1.0 to 2.0 are often quoted.