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You are here: Home > Materials > Fasteners for Plastics vs Standard Screws
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Materials

  For Aluminum

  For Magnesium

  For Plastics

    - Plastic vs Standard

    - Properties of Plastics

    - Installation

    - Design Issues

    - Fastener Selection

    - Threaded Fastener Selection

  For Sheet Metal

  For Steel







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Fasteners for Plastics vs Standard Screws

Maximize performance, prevent boss damage and increase resistance to pull-out.

Narrow thread profiles maximize performance

Tapping screws 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. This in turn maximizes fastener performance.

Because radial stress is reduced, special fasteners for plastics allow the use of smaller bosses than standard screws.

Using smaller bosses can reduce your overall costs through decreased material usage and molding cycle times.

Lowered radial stress prevents boss damage

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 subsequent damage. The plastic boss with a special fastener for plastics shows reduced radial stress.








Increased resistance to pull-out

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

Because the special fastener for plastics has a smaller minor diameter (mø) and a higher thread profile, it contains a larger volume of material (CM) and has a larger axial shear area.

This greater area of thread engagement means the special fastener for plastics is more resistant to pullout.
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