Fastshifter Bulb Self-Tapping Screw C4 4.2×40mm – 1 pcs

The Fastshifter Bulb self-tapping screw 4.2 × 40 mm is used to fix decking clips and hidden fasteners into galvanised steel joists. It is self-drilling, so no pre-drilling is required in the joist profile, and its low-profile bulb head sits flush inside the clip.

Material: C4 carbon steel, black, driven with a T15 bit. Supplied as 1 pcs.

Key features

• 4.2 × 40 mm — sized for standard clip and joist combinations.
• Self-drilling point — no pre-drilling in galvanised steel joists.
• Bulb head seats neatly in the fastener, keeping boards flat.
• C4 carbon steel, black for corrosion resistance and a discreet finish.
• T15 drive for good torque transfer and low cam-out.
• Suitable for exterior use in wet and exposed conditions.

Where it is used

• Fixing hidden decking clips into galvanised steel joists.
• WPC and composite decking on metal substructures.
• Soft, dimensionally stable timber boards such as thermally modified pine.
• Terrace, balcony and roof deck installations.

The C4 coating is matched to galvanised steel joists: it resists the corrosion that occurs where dissimilar metals meet, and keeps the fixing point protected for the life of the deck.