STAINLESS STEEL HEXAGON HEAD SELF TAPPING BT SCREWS WITH 16MM SEALING WASHER

Hexagon Head Self Tapping BT Screws with 16mm Sealing Washer — Not every fixing in this range is self-drilling - this is a self-tapping design, meaning it forms its own mating thread as it's driven but needs a pre-drilled or pre-punched pilot hole to get started, rather than boring its own hole through the steel the way a Tek-pointed screw does. That makes it the right choice wherever the hole already exists, or where the material is thin enough - sheet metal, trims, flashings, and similar light components - that a full self-drilling point is unnecessary cost and complexity. The 16mm bonded sealing washer closes the fixing point against water ingress, so this is intended for external applications in the same way as a washered Tek screw, just without the drilling capability built into the point. Applications sit around flashings, trims, light sheet-metal components, and any pre-punched fixing point on an external roof or wall detail where the hole is already formed by design rather than needing to be drilled on site. It shares the bi-metal principle used across the wider range for the same underlying reason: the stainless body and thread give long-term corrosion resistance to a fixing that's often used on visible, weather-exposed trim work, while a hardened point still gives reliable thread-forming performance into the pre-formed hole. Choosing this over a Tek 2 screw is really a question of whether a pilot hole already exists or is easy to form as part of the wider installation - where it does, a self-tapping screw is simpler and often lower cost than specifying a full self-drilling point that's never actually going to need to drill. Where no pilot hole exists and forming one isn't practical on site, a Tek-pointed screw from elsewhere in the range removes that extra step. Getting hole diameter right matters more here than on any self-drilling screw, since too large a pilot hole gives poor thread engagement and too small risks the screw failing to seat properly.

FAQs
What does "self-tapping" mean here, as distinct from "self-drilling"?
Self-tapping screws form their own thread as they're driven but need a pre-drilled or pre-punched pilot hole to start; self-drilling (Tek) screws create the hole and the thread in one operation.

How does this differ from the Bi-Metal Tek 2 range?
The Tek 2 screws have a hardened self-drilling point for fixing into steel without a pilot hole; this self-tapping range relies on a pre-formed hole and a hardened point suited to forming its own thread once started.

Is there a recognised standard behind screws of this type?
Self-tapping, thread-forming screws of this kind are commonly specified against recognised DIN or ISO thread-forming standards; the exact reference should be checked against the specific product's technical data rather than assumed.

What size pilot hole is needed?
Hole diameter needs to be matched to the screw's thread size and the material thickness being fixed, following the fastener manufacturer's recommended pilot hole guidance for the material involved rather than a generic figure.