Selection Guide

Screw Class Selection Guide (Class 1–5)

Choosing the right screw class ensures the best performance and corrosion resistance for your application. Use this simple guide to select the right one:

 

Class 1 – General Indoor Use

  • Material: Heat-treated carbon steel
  • Marking: Z
  • Best for: Dry, indoor environments where corrosion exposure is minimal.

 

Class 2 – Light Outdoor or Covered Use

  • Material: Heat-treated carbon steel
  • Marking: Z2
  • Best for: Light outdoor or sheltered areas where limited moisture exposure may occur.


Class 3 – Moderate Outdoor Use

  • Material: Mechanically galvanised carbon steel
  • Marking: Z3
  • Best for: Outdoor structures and moderate weather exposure.


Class 4 – Heavy-Duty Outdoor Use

  • Material: Mechanically galvanised carbon steel
  • Marking: Z4
  • Best for: Harsh outdoor or industrial environments requiring high corrosion resistance.


Class 5 – Marine & Coastal Use

  • Coating: Zinc clear coating on 304-grade stainless steel
  • Material: Stainless steel (bi-metal option with carbon steel drill point)
  • Marking: Z5
  • Best for: Coastal, marine, or high-moisture environments where maximum corrosion protection is needed.


Roof Type Selection Guide

  • Corrugated Roof Sheeting (AZ150 and AZ200) ISO class 3 and 4 environments.

    Fixing onto steel purlins.

    Recommended ZAP roofing fasteners.

    Class 3 or Class 4 metal.

    • 12 (5.5mm) x 38mm Hex Flange with Seal
    • 12 (5.5mm) x 50mm Hex Flange with Seal

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    Fixing onto timber purlins.

    Recommended ZAP roofing fasteners.

    Class 3 or Class 4 timber.

    • 12 (5.5mm) x 65mm Hex Flange with Seal
    • 12 (5.5mm) x 75mm Hex Flange with Seal

    ________________

    Side Cladding – Size: 12 (5.5mm) x 25mm Hex Flange + seal Class 3 or 4

     Roof Flashing + Ridge Caps – Size: 14 (6.3mm) x 22mm Hex Flange + Seal Class 4

  • IBR Roof Sheeting AZ150 AZ200 ISO Class 3 And Class 4 Environments

    Fixing onto steel purlins.

    Recommended ZAP roofing fasteners.

    Class 3 or Class 4 metal.

    • 12 (5.5mm) x 65mm Hex Flange with Seal

    ________________

    Fixing onto timber purlins.

    Recommended ZAP roofing fasteners.

    Class 3 or Class 4 timber.

    • 12 (5.5mm) x 85mm Hex Flange with Seal T17

    ________________

    Side Cladding – Size: 12 (5.5mm) x 25mm Hex Flange + seal Class 3 or 4

     Roof Flashing + Ridge Caps – Size: 14 (6.3mm) x 22mm Hex Flange + Seal Class 4

  • Industrial 7 Aluminium ISO Class 5 Environments.

    Fixing onto steel purlins.

    Recommended ZAP roofing fasteners.

    Class 5 304 bi metal

    • 12 (5.5mm) x 65mm Hex Flange with Seal

    ________________

    Fixing onto timber purlins.

    Recommended ZAP roofing fasteners.

    Class 5 304 bi metal

    • 12 (5.5mm) x 85mm Hex Flange with Seal T17

    ________________

    Side Cladding – Size: 12 (5.5mm) x 25mm Hex Flange + seal Class 5

     Roof Flashing + Ridge Caps – Size: 14 (6.3mm) x 22mm Hex Flange + Seal Class 5
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