Aviation fastener is no stranger, its role is to connect thousands of aircraft parts to form a whole; The load is transferred and the deformation is coordinated in the diameter of parts. Today, we will learn more about the basic knowledge of aviation fasteners.
Threaded fasteners
Threaded fasteners: bolts, screws, washers and nuts
Helix -- a moving point on the surface of a cylinder, rotating at constant speed around the axis while moving at constant speed along the axis.
Thread - the plane figure moves along the helix, and the thread is obtained by keeping the figure through the axis of the cylinder.
Thread type and fit grade
1、 Thread type
Standard: American National coarse
American National Fine
American Standard United Coarse
American Standard United Fine
Differences: 1. The same size and number of coarse thread series and fine thread series have the same thread nominal diameter, but the number of teeth per inch of length is different.
2. The distribution of tolerance is different; There are also different requirements for threads with a diameter of 1 inch:
NF regulation - 14 teeth per inch, expressed as 1-14nf
UNF rule - 12 teeth per inch, expressed as 1-12unf
2、 Matching grade
There are also grades for threads. The grade of thread indicates the fit tightness of thread pair. It has five grades:
Level 1 - loose fit (the nut can be easily turned by fingers)
Level 2 - free fit (for aviation screws)
Grade 3 - medium fit (used for most aviation bolts)
Level 4 and 5 - tight fit (the nut can only be screwed on with wrench)
The higher the grade number is, the tighter the thread pair fits.
