Duro PT Series
The Duro PT® Screw is a direct screw fastener for use in thermosetting plastics. The design incorporates many unique features which provide designers with a really effective direct screw fixing for these materials. The cutting notch combined with the profiled thread root and special thread form provides low installation and high stripping torques. The efficient removal of cutting debris ensures greatly reduced bursting forces, providing the solution to a common problem associated with conventional self-tapping screws, when used in thermosets.
Advantages
- Reduces stress in thermosetting plastics to an absolute minimum
- Wide safety margin between installation and stripping torque
- Suitable for all types of thermosetting plastics.
- Can be used in thermoplastics with a high fill content (>30%)
Duro PT Design Features
Special Cutting Notch
The cutting notch helps remove material during insertion, reducing installation effort and minimizing stress on the plastic. The profiled root helps with debris removal and allows space for cut plastic.
- Removes 60-80% of material cut during the thread cutting operation
- Reduces installation torque
- Reduces radial pressure
Special Profiled Root
Thread geometry is shaped to balance low drive torque with strong stripping resistance—this ensures that once engaged, the threads hold well even under load or vibration.
- Provides space for debris
- Reduces radial stress
- Reduces installation torque
- Increases stripping torque
Special Shaped Tooth
The shape, notch, and profile are designed to limit outward pressure (“bursting force”) in the boss on thermosets, which otherwise risk cracking or failure.
- Reduces radial stress
- Maximum surface bearing area
- High stripping torque
- High clamping force
- High back-off torque
Design Guide
Boss design depends on the following factors:
- Type of thermoset material used
- The density of the material
- The amount and type of filler
Because of these variables the following recommendations are minimum and maximum guidelines only.
Dimensions
PRODUCT CODE WN 17
HEAD STYLE 42 Pan
HEAD STYLE 43 Countersunk
Standard Recess Styles
Other available recesses are shown on optional features page.
Size Range
Material
Case Hardened Mild Steel
Standard Finishes
Zinc Plate and Clear Passivation (Z)
Zinc Plate and Chromate (ZC)
Zinc Plate and Black Chromate (ZBC)
Other Finishes
Possible on quotation
How to Specify
Duro PT Key Features & Design Elements
Cutting notch + profiled thread root: The cutting notch helps remove material during insertion, reducing installation effort and minimizing stress on the plastic. The profiled root helps with debris removal and allows space for cut plastic.
Special thread form: Thread geometry is shaped to balance low drive torque with strong stripping resistance—this ensures that once engaged, the threads hold well even under load or vibration.
Reduced radial stress: The shape, notch, and profile are designed to limit outward pressure (“bursting force”) in the boss on thermosets, which otherwise risk cracking or failure.
Compatibility with filled thermoplastics: While optimised for thermosets, Duro-PT® screws can also be used with thermoplastics having high filler content (>30%), giving flexibility in materials choice.
Design & Application Guidelines
Boss & holes setup
- Use bosses with sufficient wall thickness to resist cracking; generally, boss diameter should be approx. 2.5× to 3× the nominal screw diameter.
- Hole diameter measured at the mid-penetration of the screw should be controlled (roughly 0.85-0.88× the external thread diameter) to allow proper cutting and engagement.
- Provide lead-in chamfers or moulded entry transitions to reduce initial damage and easing screw start.
Installation torque control
Tighten gradually, allowing the cutting notch to engage without excessive torque.
Avoid excessive over-drive, which can damage threads or strip bosses.
Material selection & environmental effects
Thermosetting plastics are often brittle; incorporate fillers, reinforcements, or additives that improve toughness.
Consider temperature, moisture, UV exposure; coatings or finishes on screws may help protect both screw and plastic.
Reusable & vibration performance
These screws can maintain holding strength under repeated installation cycles if the thread root, notch, and thread form are not overloaded.
Vibration resistance is increased due to the locking friction generated in the special thread form.
Advantages & Common Use Cases
Effective for high-rigidity applications where thermosets are required (e.g. components in electrical insulation, circuitry boards, industrial housings).
Helps reduce the risk of cracking or failure in thermoset bosses by keeping radial stresses low.
Allows thinner walls or smaller bosses compared to plain cutting screws, reducing material cost and weight.
Beneficial in mixed assemblies where both thermosets and filled plastics are present.
Enhance Your Assembly with Our Precision Duro PT Screws
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