STAINLESS STEEL HEXAGON HEAD BI-METAL TEK 3 SCREWS WITH 16MM SEALING WASHER

Hexagon Head Bi-Metal Tek 3 Screws with 16mm Sealing Washer — This is the washered counterpart to the bare Tek 3 hex screw, built for exactly the situation the unwashered version isn't: fixing profiled steel roofing or cladding sheet through to a medium-gauge purlin or rail, where the screw penetrates the external weather skin and that penetration has to be sealed. The 16mm bonded washer compresses against the sheet profile to close the hole against wind-driven rain, and it's sized generously enough to spread clamping load without crushing or distorting the sheet at the fixing point. Applications sit squarely in roofing and cladding installation on steel-framed industrial, agricultural, and commercial buildings - anywhere a profiled sheet needs a primary structural fixing into the purlins or rails beneath it. Bi-metal construction runs through the whole Tek range for the same reason here as elsewhere: the stainless body and thread give the fixing the weather resistance an external roof or wall penetration needs over the building's life, while a hardened carbon-steel point brazed to the tip does the actual work of self-drilling and self-tapping into the steel purlin, which a plain stainless point can't manage reliably at this drilling capacity. Point rating is the main technical decision when specifying this screw: Tek 3 sits in the middle of the range, suited to medium-gauge purlins and rails that are heavier than light stud-gauge steel but lighter than the thick structural sections a Tek 5 point is built for. If the point struggles to start, stalls partway through, or takes noticeably longer to drill than expected, the purlin is probably a heavier section than Tek 3 is rated for and the Tek 5 washered equivalent is the correct upgrade. Length should be sized to clear the sheet profile height plus full engagement in the purlin, and the washer should always be checked for full, even compression against the sheet once driven, since an under- or over-driven washer is a common cause of roof leaks at the fixing point.

FAQs
How can you tell if the washer has compressed correctly when driving?
A properly driven washer sits evenly compressed against the sheet profile with no visible gap or excessive dishing; under-driving leaves a gap that can leak, while over-driving can crush the washer or dish the sheet.

Can the washer be reused if the screw needs to be removed and re-driven?
It's generally best practice to fit a new screw and washer rather than reuse one that's already been compressed, since a washer that's already taken a full seal won't necessarily compress evenly a second time.

How does this compare with the Tek 5 washered version?
Both are washered hex-head fixings for external sheet-to-steel connections using the same 16mm washer format; Tek 5 has the greater drilling capacity and longer point for thicker steel sections, where this Tek 3 version suits medium-gauge purlins and rails.