STAINLESS STEEL POZI RAISED COUNTERSUNK WOODSCREWS 20MM SEALING WASHER

Pozi Raised Countersunk Woodscrews 20mm Sealing Washer — This is the mid-size option in the sealing washer range, built for the same job as its 15mm and 25mm siblings — fixing exterior timber boards such as fascia, soffit, and cladding where water tracking down into the clearance hole needs to be stopped at the fixing point — but with a larger washer for boards or holes that the 15mm size doesn't comfortably cover. As the screw is driven, the bonded washer beneath the raised countersunk head compresses against the board, closing the gap around the hole; a bigger washer simply spreads that seal, and the load it carries, over a wider area, which matters on thicker boards, larger clearance holes, or softer sheet materials that could otherwise let a smaller washer pull through under stress. The raised countersunk head sits slightly proud once driven, following the same base geometry used across this product family, and is driven with a Pozidriv recess, which handles routine exterior fixing well without the extra cost of a hexalobular drive — sensible unless the job involves sustained high-volume power-tool driving. Grade selection follows the same logic as any exterior timber fixing: A2 (304-equivalent) is the right specification for general UK weather exposure, while A4 (316-equivalent) earns its higher price where the building faces the coast, sits near a swimming pool, or is otherwise exposed to elevated chloride levels, since A4 resists the pitting corrosion that A2 will eventually show in those conditions. Deciding between the 15mm, 20mm, and 25mm washer sizes mostly comes down to board thickness and hole diameter — the 20mm size is a sensible default where boards are moderately thick or spaced closely enough that a very wide washer would start to interfere with neighbouring fixings, while gauge and length still need matching to the substrate to ensure solid thread engagement beneath the board.

FAQs
What's the practical difference between the 15mm and 20mm washer sizes?
20mm gives a wider sealing and load-spreading area, useful for thicker boards or larger clearance holes; 15mm is more discreet and suits thinner boards or where a smaller washer footprint is preferred.

When would 25mm be a better choice than 20mm?
25mm is worth choosing where board thickness, hole size, or the compressibility of the sheet material is at the higher end of what needs supporting — it gives the widest sealing footprint of the three, at the cost of being the most visually prominent.

Does a bigger washer make the screw stronger?
It spreads clamping load over a wider area and reduces the risk of pull-through, but the overall strength of the fixing still depends on screw gauge, length, and how well it engages the substrate, not washer size alone.

Is this screw suitable for both fascia and cladding fixing?
Yes, it's a general-purpose exterior board fixing suited to fascia, soffit, cladding, and roofing trim wherever a sealed, weathertight fixing point is needed.