STAINLESS STEEL HEXALOBULAR RAISED COUNTERSUNK WOODSCREWS 25MM SEALING WASHER

Hexalobular Raised Countersunk Woodscrews 25mm Sealing Washer — This is the largest washer in the hexalobular sealing washer range, combining the widest sealing footprint available in this product family with a drive built for high-torque, high-volume driving — the pairing suited to exterior fixing jobs where both board thickness and installation speed are demanding. The bonded washer beneath the raised countersunk head compresses against the board as the screw seats, closing the gap around the clearance hole against water ingress; at 25mm it gives the broadest coverage of the three sizes offered, which is worth choosing specifically where boards are thick, holes are larger than standard, or the sheet material is soft enough that a smaller washer risks being pulled through under load. Hexalobular is the drive throughout this range because exterior cladding and fascia work is typically driven in volume with a powered site tool, and the extra contact faces in a hexalobular recess resist cam-out and wear far better than Pozidriv under that kind of sustained torque — the difference becomes more noticeable the more screws are driven per job. Grade selection follows the same logic as elsewhere in the range: A2 (304-equivalent) is the right and more cost-effective specification for general UK exterior exposure, while A4 (316-equivalent) earns its higher price on coastal buildings, cladding facing salt spray, or fixings near swimming pools, where its added resistance to chloride pitting protects the fixing well beyond what A2 offers in those harsher conditions. Whether a larger washer actually improves weather sealing depends partly on installation: correct driving torque and full, even compression of the washer against the board matter as much as washer diameter, so gauge and length still need to be matched to the substrate to ensure solid thread engagement beneath the board, not just the washer size alone.

FAQs
How does this compare to the 15mm and 20mm hexalobular versions?
All three share the same head shape and hexalobular drive; only the washer diameter changes, scaling sealing area and visual prominence from most discreet (15mm) up to widest coverage (25mm).

How does this compare to the Pozi 25mm version?
Washer size and sealing function are the same; the hexalobular drive is generally preferred for power-tool-driven installation across larger areas such as a full cladding run, since it resists cam-out more consistently.

Does washer size alone determine weather sealing performance?
No — installation matters just as much: correct driving torque and even compression of the washer against the board are needed for a reliable seal, regardless of washer diameter.

Is the 25mm washer worth using as a default for all exterior board fixing?
Not necessarily — it's the right choice for thicker boards or larger holes, but for standard boards the 15mm or 20mm washer seals just as effectively with a less prominent finish.