STAINLESS STEEL POZI RAISED COUNTERSUNK WOODSCREWS 25MM SEALING WASHER

Pozi Raised Countersunk Woodscrews 25mm Sealing Washer — The 25mm washer is the largest in this sealing washer range, built for exterior board fixing where a smaller washer risks pulling through — softer or more compressible sheet materials, thicker boards, or larger clearance holes that need the widest possible load-spreading and sealing footprint the range offers. The principle is the same across all three sizes: a bonded rubber or EPDM washer sits beneath a raised countersunk head and compresses against the board surface as the screw is driven, closing the gap around the hole that would otherwise let water track down into the timber or substrate beneath — fascia, soffit, cladding, and roofing accessories are the typical applications. Choosing 25mm over the 15mm or 20mm options is really a trade-off between coverage and visibility: it gives the broadest sealing area and the best resistance to pull-through on demanding boards, but it's also the most visually prominent washer of the three once installed, so it's worth reserving for boards that genuinely need that extra support rather than using it as a default. The head follows the same raised countersunk geometry as the rest of the range and is driven with a Pozidriv recess, a sound middle-ground choice for hand or light power-tool driving; where the job involves high-volume or impact-driver installation across a full cladding run, the hexalobular version of this same washer size resists cam-out more reliably under sustained torque. On grade, A2 (304-equivalent) handles the great majority of UK exterior exposure without issue, while A4 (316-equivalent) is worth the extra cost for coastal buildings, cladding near swimming pools, or anywhere road salt or chloride exposure is elevated, since it resists the pitting corrosion A2 can eventually develop there. Gauge and length should still be chosen to give solid thread engagement in the material beneath the board, independent of washer size.

FAQs
Is a bigger washer always the safer choice?
Not necessarily — a 25mm washer is the right choice for boards or holes that need the extra coverage, but for thinner boards or smaller holes it's an unnecessarily large, more visible washer where the 15mm or 20mm size would seal just as effectively.

Does washer size affect how the screw drives?
No — driving characteristics come from the head, thread, and drive type, which are the same across all three washer sizes; only the washer diameter changes.

Should I use the 25mm washer near board edges?
It can be, though a wide washer close to a board edge may not seat fully flat if the board's edge profile interferes with it — checking that the washer sits fully on the board surface is worth doing before committing to it across a full run.

How does this compare to the hexalobular 25mm version?
Head, washer, and sealing function are identical; the hexalobular version simply gives better resistance to cam-out under sustained power-tool or impact-driver use.