STAINLESS STEEL HEXALOBULAR RAISED COUNTERSUNK WOODSCREWS 20MM SEALING WASHER

Hexalobular Raised Countersunk Woodscrews 20mm Sealing Washer — The 20mm hexalobular sealing washer screw sits in the middle of this range, pairing a mid-size bonded washer with a drive built to handle high-volume, power-tool-driven exterior fixing. As with the rest of the range, the washer compresses under the raised countersunk head as the screw is driven, sealing the clearance hole against water tracking into the board or substrate beneath — the core requirement for fixing fascia, soffit, and cladding boards outdoors. Twenty millimetres gives more sealing and bearing area than the 15mm option, which matters where clearance holes are a little larger or boards a little thicker, without moving up to the widest and most visually prominent 25mm washer. Hexalobular is the drive of choice throughout this range rather than Pozidriv specifically because exterior board fixing is usually done at volume — a full cladding elevation might mean hundreds of screws driven with an impact driver or powered site tool — and the extra contact points in a hexalobular recess resist cam-out and wear far better under that kind of sustained, repeated torque. Grade should be chosen the same way as any exterior timber fixing: A2 (304-equivalent) handles typical UK weather exposure reliably and is the right specification for the majority of fascia and cladding work, while A4 (316-equivalent) is worth the added cost specifically for coastal sites, buildings exposed to salt-laden air, or cladding near swimming pools, where A4's molybdenum content resists the chloride pitting A2 can eventually develop. Choosing this washer size over the 15mm or 25mm alternatives comes down to board thickness and hole diameter on the specific job, and it's worth settling that decision — along with screw gauge and length for solid thread engagement in the substrate — before starting a large fixing run rather than mixing washer sizes partway through.

FAQs
How does this compare to the Pozi 20mm version?
Washer size and head shape are identical; the hexalobular drive offers better cam-out resistance and torque handling, which matters for sustained or high-volume power-tool driving.

When should I use hexalobular rather than Pozi for exterior fixing?
Hexalobular is generally the better choice wherever fixings are driven with an impact driver or in large numbers, since the recess resists wear and cam-out more reliably than Pozidriv over repeated use.

Is 20mm the right default washer size if I'm not sure?
It's a reasonable mid-point choice for typical board thicknesses and clearance holes, though checking the specific board and hole size against the 15mm and 25mm options is worth doing before ordering a large quantity.

Does washer size need to match across a whole job?
It's good practice to keep washer size consistent across a run for a uniform finish and predictable sealing performance, rather than mixing sizes based on availability.