PT Alternative Screw Product Analysis:
Continuous Innovation of Plastic Fasteners
Origin and Core Design
PT screw was developed in the 1990s by the German company EJOT specifically for plastic applications. It solved problems such as plastic cracking, stress concentration, and unreliable connections caused by traditional screws.
The design philosophy is based on a profound understanding of the flow characteristics of thermoplastic materials. Unlike traditional screws for metal, its special geometry takes into account plastic’s creep characteristics, recovery behavior, and stress distribution patterns. The design goal was to minimize stress on the surrounding material while forming internal threads, thereby ensuring connection reliability and long-term stability.
This innovative design not only improved product quality but also reduced production costs by decreasing the need for metal inserts。
Its two core design features are:
1 30°thread angle：
Compared to traditional screws with a 60-degree thread angle, the steeper 30-degree thread profile enables deeper engagement with plastic materials, increasing thread engagement depth and significantly improving pull-out resistance and anti-loosening performance.
This design allows radial stress to be distributed evenly, avoiding stress concentration that leads to base material cracking.
2 Double Core Diameter:
This design features a deeper thread root diameter that provides ample space for displaced material, reducing compressive stress on the surrounding material during thread forming. As a result, material can flow more naturally, forming a more uniform thread structure while reducing installation torque requirements. This design is particularly beneficial for thin-walled structures, allowing the use of thinner materials without compromising connection strength.
Force Analysis and Advantages
The unique design of the PT screw optimizes its force distribution, offering significant advantages.
- Low Radial Stress:
The double core diameter absorbs displaced material, avoiding excessive expansive force on the plastic hole wall, fundamentally preventing cracking.Traditional self-tapping screws, lacking sufficient space to accommodate this displaced material, tend to cause excessive material compression and stress concentration, while PT screw’s design allows material to flow and redistribute more freely, forming a more uniform stress field.
This design is particularly beneficial for brittle materials like glass-fiber reinforced plastics, as these materials are more sensitive to stress concentration.
- High Vibration Resistance:
The 30° angle and large contact area provide excellent self-locking and anti-loosening performance. When load is applied to the connection point, stress can be smoothly transferred to the entire contact area rather than being concentrated at a few points. This uniform stress distribution significantly improves long-term load capacity and reduces creep relaxation, especially in thermal cycling and vibration environments.
- High Reusability:
Forms threads rather than cutting them, causing minimal damage to the material, allowing for up to 40 repeated installations and removals.
Comparison of Differences
1. PT vs. PLASTITE
Although both PT screws and Plastite screws are self-tapping screws for plastics, they have significant differences in design philosophy, technical characteristics, and performance. Plastite screws are another trilobe thread type of thread forming screw designed for plastics, but their design focuses more on versatility, while PT screws are specifically optimized for thermoplastic materials.
Another important difference is material selectivity. PT screws are specifically optimized for thermoplastic materials and perform extremely well in engineering plastics such as polyamide (PA), polycarbonate (PC), ABS, and POM. Plastite screws have a more versatile design suitable for a wider range of plastic materials, including some thermosetting plastics, but they are not as optimized for specific high-performance engineering plastics as PT screws.
These two types differ in thread design, stress distribution, and application range.
| FEATURES | PT SCREW | Plastite SCREW |
| Thread Angle | 30° | Typically 45° or 60° |
| Design Focus | Optimized for thermoplastics, low stress | Versatility, compatibility |
| Pull-out Resistance | Higher | General |
2.PT vs. DELTA PT vs. EVO PT
DELTA PT and EVO PT are evolved versions based on PT.
DELTA PT （around 2000）: Introduced a multi-angle thread profile, further optimizing material flow. Torque and pull-out resistance improved by up to 50% over the original PT.
EVO PT （around 2019) : Focuses on installation process optimization and digitalization, providing depth-independent torque and CAE simulation support, ideal for automated production.+
Conclusion
As the use of plastic materials continues to grow across various industries, the demand for efficient and reliable connection solutions will also continue to increase.
For design engineers and product developers, understanding the technical characteristics and application scenarios is crucial. Correctly selecting and applying appropriate fastening technology can significantly improve product performance, reduce production costs, and enhance market competitiveness.
Whether in the automotive industry, electronic products, home appliance equipment, or emerging smart products, PT screw technology will continue to play a key role in connecting innovation with reality.
MORE DETAIL MECHANICAL AND CHEMICAL INTRODUCTION PLEASE FIND :
https://engineeringproductdesign.com/knowledge-base/self-tapping-screws-for-plastics/
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