Type B,type AB and other standard fasteners have a wide thread profile (also called flank angle) of 60°Special fasteners for plastics have special thread profiles to meet the needs of these unique materials.These narrower thread profiles,ranging from 30°to 48°,reduce radial stress and expansion.

Because radial stress is reduced,special fasteners for plastics allow the use of smaller bosses than standard screws,as shown of left.Using smaller bosses can reduce your overall costs through decreased material usage and molding cycle times.

     

 

   In the illustrations at left,CM represents the area subjected to shear when an axial load is applied.

Because the special fastener for plastics has a smaller minor diameter(m) and a larger volume of material (CM) and has a larger axial shear area.This greater raea of thread engagement means the special fastener for plastics is more resistant to pull-out.

 

Radial force（FRAD）is an undesirable force since it creates outward stress and can damage the boss.

Although the same volume of material is displaced between the 60°thread and the 30°thread,the radial force generated by the 30°thread is approximately one-half that of the 60°thread.

In the photo at right,the plastic boss with a 60°thread fastener shows radial stress and subseguent. The plastic boss with a special fastener for plastics shows  reduced radial stress.