PT Type DG
The PT Type DG is a direct screw fastener for use in light alloys.
The design incorporates many unique features which provide designers with a really effective direct screw fixing for these materials.
The profiled thread root gives low installation torque whilst the special thread form provides high stripping torque.
Advantages
- Thread forming - No debris
- Reliable & easy installation into punched, drilled, extruded & moulded holes
- Reusability of screw
Design Features
Special Profiled Root
The PT Type Screw is shaped to allow material flow, aiding in smooth formation and reduced stress.
- Reduces stress
- Allows material to flow during thread forming
- Reduces installation torque
- Increases pull-out load
Special Shaped Tooth
It provides low installation torque in light alloys while maintaining high stripping torque for reliability.
- Reduces radial stress
- Maximum surface bearing area
- High stripping torque
- High clamping force
- High back-off torque
Design Guide
Soft materials = ≤ 50 vpn
Medium soft materials = 51 to 75 vpn
Hard materials = 76 to 100 vpn
For specific application advice, contact PSM.
Hole & Boss Dimensions
- Use a slight taper (~1° inclusive) in the hole for smooth insertion.
- Optimize hole diameter at the mid-penetration point for effective thread forming.
- Minimum boss diameter is generally about 2.5 × d (nominal thread diameter).
- Recommended screw penetration ranges between 1.5 × d and 2.5 × d depending on material hardness.
Material & Load Factors
For soft alloy castings or thin walls, ensure the boss and surrounding geometry can withstand stresses during installation.
In plastic regions, include ribs or reinforcements to prevent deformation.
Installation & Torque Control
Drive the screw gradually to allow proper thread forming without jamming.
Avoid over-torquing to prevent stripping or cracking.
Use torque-controlled drivers at recommended speeds to reduce heating or damage.
Hybrid Assembly Tips
For plastic-metal assemblies, sequence screw insertion to suit structural needs.
Validate that forming in one material doesn’t compromise performance in the other.
Dimensions
How to Specify
Applications & Advantages
PT Type DG is ideal for hybrid assemblies such as lighting housings, enclosures with metal frames and plastic covers, and brackets attached to die castings. Its advantages include:
Unified fastening solution across metal and plastic
Simplified inventory and assembly
Strong thread performance in light alloy
Resistance to vibration and relaxation
Reduction in part count and assembly errors