STAINLESS STEEL HEXAGON HEAD SELF DRILLING WITH SEALING WASHER

Hexagon Head Self Drilling with Sealing Washer — This screw pairs a standard external hexagon head with a separate bonded sealing washer fitted captive beneath it, so instead of relying on a metal flange to spread load, the washer compresses against the fixed sheet to close the hole against water and air ingress. It's the natural choice for roof and wall cladding, external HVAC ductwork, and any steel-to-steel or steel-to-timber fixing exposed to weather, condensation, or washdown, where DIN 7504K's plain metal washer head would leave the fixing point unsealed. As with all stainless self-drilling screws, the drilling point is typically a hardened 410 or 420 martensitic stainless rather than a true austenitic A2 or A4 body throughout - austenitic grades resist corrosion well but won't harden enough to drill and tap steel in one pass, so the point is a different, harder alloy even on a stainless-bodied screw. For most external building envelope work, A2-equivalent corrosion resistance on the shank, head, and washer is adequate; A4 becomes worth the extra cost close to the coast, near swimming pools, or wherever chloride exposure or frequent washdown would otherwise shorten the service life of an A2 fixing. Sizing follows the same logic as any self-driller: the point rating needs to cover the full thickness of steel being drilled, with enough remaining thread length to engage properly once through, and the washer diameter should suit the profile and hole tolerance of the sheet being fixed so it seats flat rather than bridging a rib or seam. There's no separate DIN number for this specific configuration - it's typically specified against the equivalent hex-head self-drilling standard with the sealing washer noted as an addition, so confirming washer material (commonly EPDM-faced) and bond quality with the supplier is worthwhile where sealing performance is critical to the specification.

FAQs
Does the washer need to be checked over the life of the fixing?
Bonded EPDM-faced washers are designed for long outdoor exposure, but UV and repeated thermal cycling can eventually harden or crack the rubber face. A periodic visual check as part of routine roof or cladding maintenance is worth building in, since the washer can't be replaced separately once bonded to the head.

What drive type does it use?
An external hexagon head, driven with a socket rather than a bit, matching standard hex driver sizes.

Is this the same as fitting a loose washer under a plain-head self-drilling screw?
No - the sealing washer here is bonded and captive under the head at manufacture, giving a controlled, consistent compression seal. A washer added on site under a plain head won't bond or compress the same way.