Origin of Direct Fastening in Plastics
The PT® Screw – How EJOT Revolutionized Screw Connection in Plastics
The PT® Screw – How EJOT Revolutionized Screw Connection in Plastics
With the PT® Screw (PT stands for "Plastic Thread"), EJOT laid the technological foundation for direct screw connection in thermoplastic materials as early as the late 1970s.
At a time when plastics were increasingly replacing metal, creating a secure, load-bearing screw connection in plastic was considered technically unfeasible in terms of process reliability.
The solutions used at the time—metal threaded inserts, embedded parts, or overmolded nuts—were functional but:
- cost-intensive
- labor-intensive to install
- problematic regarding weight and process efficiency
The PT® screw took a new approach: a thread geometry optimized for plastic that, unlike the sheet metal screws commonly used at the time, created a load-bearing mating thread directly within the thermoplastic during installation—without damaging the material.
This made reliable direct screw fastening possible for the first time, eliminating the need for costly metal inserts.
The PT® screw quickly established itself as the benchmark solution for plastic screw connections and made EJOT a technological pioneer in this field.
DELTA PT® – The Key Development Step for Industrial Applications
The rapid growth of the plastics industry, combined with increasing load requirements and higher expectations in terms of process reliability and series production capability, meant that the original solutions could no longer cover all applications—especially as fiber-reinforced engineering plastics entered the market.A decisive milestone in the further development of PT® technology was therefore the DELTA PT® screw.
It transferred the core principle of the PT® screw to more demanding industrial applications and set the technological benchmark in direct fastening in plastics for many years, becoming the market leader in this segment.
With its advanced thread geometry, it offers:
- higher mechanical load capacity
- reliable assembly characteristics
- outstanding process reliability in mass production
In practice, DELTA PT® proved itself across numerous industries as a high-performance, economical, and robust fastening solution for thermoplastics.
It clearly demonstrated that plastic fastenings can be not only assembly-friendly and cost-efficient, but also:
- highly load-bearing
- precisely designable using calculation tools
- reliably controllable in industrial production
This made DELTA PT® the technological link between the original PT® screw and today’s EVO PT® generation.
EVO PT® – State of the Art in Direct Fastening in Plastics
The result of this continuous, application-driven development is the EVO PT® screw.It represents the latest and most powerful evolution stage of the PT® family and has been specifically developed to meet the demands of modern designs:
- new and glass fiber reinforced thermoplastics
- increasing requirements due to vibration, temperature, and service life
- lightweight and hybrid constructions
- automated assembly processes
- rapid prototyping using 3D printing
The EVO PT® screw combines:
- a biomimetically optimized thread geometry
- improved load distribution in the plastic
- higher clamp loads and pull-out values
- enhanced fatigue strength under dynamic loading
It is significantly more powerful than previous PT® variants and conventional plastic screws – and defines today’s global reference standard.
Conclusion for Users, Designers & Engineers
The development of the PT® family shows a clear technological progression:from fundamental innovation to industrial maturity and finally to today’s high-performance solution.
👉 The EVO PT® screw is the result of this evolution – and the most reliable, efficient, and high-performance solution for direct fastening in plastics today and in the future.
The Technical Concept Behind the PT® Screw
The PT® screw was the first screw specifically designed for plastics, characterized by a plastic-optimized thread geometry.It creates a form-fit and friction-fit joint by forming a load-bearing internal thread directly in the thermoplastic during installation.
For the first time, this enabled:
- direct fastening without a nut thread
- elimination of metal inserts
- process-reliable series assembly
The PT® screw quickly became the reference product for plastic fastening.
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Developed at EJOT in Bad Laasphe
The development of the PT® screw is closely linked to the Bad Laasphe site (North Rhine-Westphalia, Germany).At the former company Eberhard Jaeger—later EJOT Verbindungstechnik GmbH & Co. KG—engineer Hermann Großberndt worked on new fastening solutions for plastics.
Together with Kurt Ociepka, he conducted extensive testing and recognized early that:
- sheet metal and wood screws are unsuitable for plastics
- new thread profiles are required to prevent relaxation, cracking, and pull-out
The PT® screw emerged from this consistent application-driven development work.
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Scientific Foundation & Industrial Implementation
Parallel to industrial development, the University of Kassel also conducted intensive research into plastic fastening.
Through the Department of Materials Engineering/Plastics, contact was established with Stephan Weitzel, whose thesis examined the influence of thread geometry on the quality of screw joints in plastics.
This close combination of:
- scientific research
- experimental validation
- real assembly conditions
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Market Breakthrough and New Applications
In the 1980s, the PT® screw became widely established across various industries, particularly in:- household appliances
- electronics
- large containers & technical consumer goods
A major milestone was its use in television sets:
complex fastening systems with up to 28 individual components could be replaced by just four PT® screws—resulting in a significant reduction in components, weight, and cost.
The PT® screw quickly became the market and technology standard and was licensed internationally.