Self-drilling phosphate screws Koelner/Rawlplug WS 3.5 x 25 are designed for direct fastening of thin metal profiles and light-gauge sheet metal assemblies. The WS variant integrates a drill point that allows drilling and tapping in one operation without pre-drilling in many thin-metal applications. The phosphate coating provides basic corrosion resistance and improves lubricity during driving, making these screws suitable for repair tasks and small installation jobs where individual fasteners are needed.
Advantages
These screws combine a self-drilling tip with a phosphate finish to reduce installation time and improve thread engagement in thin metal. The integrated drill point eliminates the need for a separate drilling step in many cases, while the phosphate coating reduces friction and gives moderate protection against corrosion. Supplied as single units, they are convenient for one-off repairs or situations where bulk packaging is unnecessary.
Suitable for
- Fastening metal profiles to light-gauge steel or thin-sheet substrates
- Installation of framing, channels, and small metal assemblies
- Repair and maintenance where individual screws are needed
- Applications requiring drilling and tapping in one operation
When it may not be suitable
These screws are intended for thin metal and light-gauge profile work; they are not suitable for structural connections that require high shear or tensile strength. For thicker steel, concrete, masonry, or heavy-duty load-bearing applications, specialized fasteners or pre-drilling with appropriate anchors should be used. The phosphate coating offers limited corrosion protection and is not a substitute for stainless or fully galvanized fasteners in highly corrosive environments.
Key specifications
- Thread type: self-drilling, designed for metal-to-metal fastening
- Diameter: 3.5 mm
- Length: 25 mm
- Tip: integrated drill point for drilling and tapping without pre-drilling in thin materials
- Surface finish: phosphate coating for reduced friction and moderate corrosion resistance
- Drive type: compatible with common screwdrivers or bits used for metal screws
- Package quantity: single unit, suitable for repairs and small jobs
How to use
Select a suitable screwdriver or bit that matches the screw head profile and place the screw perpendicular to the metal surface. Apply steady pressure and drive at moderate speed so the integrated drill point can bore into the thin metal and form threads. Avoid excessive torque settings on power tools to prevent stripping the head or over-driving the screw. For optimal results in coated or thicker materials, check compatibility first and consider pilot holes or alternate fasteners if the screw does not advance smoothly.
What to consider before purchase
- Intended substrate: appropriate for thin-gauge metal profiles, not for thick structural steel or masonry
- Corrosion requirements: phosphate coating provides limited protection; choose stainless or galvanized fasteners for aggressive environments
- Load demands: assess whether a self-drilling screw of this size meets shear and tensile requirements for your application
- Quantity needs: sold as a single unit—order sufficient quantity for larger jobs
Usage recommendations
Use a compatible screwdriver bit and moderate torque. For repetitive installations, test on scrap material to confirm drilling and thread formation. Store in a dry place to preserve the phosphate finish and inspect each screw before use if corrosion resistance is critical.
