Self-Tapping Screw

Self-tapping screws fix aluminum or GI cladding sheets over insulation and onto structural supports. They are self-drilling hex head screws with a bonded EPDM washer, so one operation drills, fastens and seals the hole in thin sheet without pre-drilling. They are also used to close jacketing overlaps on pipes, ducts and equipment.

Self-tapping screws are available in 5.5 x 25 mm, 5.5 x 32 mm, 5.5 x 50 mm, 6.3 x 50 mm and 6.3 x 70 mm (diameter x length), with 16 mm or 19 mm washers. Short screws suit sheet-to-sheet overlaps on pipe cladding, while longer lengths are needed when fixing through to a support or frame.

Stainless steel SS 304 or SS 316 screws are the usual choice for aluminum cladding outdoors, and SS 316 is preferred in coastal, marine and chemical environments. Zinc-plated GI screws are an economical option for indoor work and GI cladding. Salt spray resistance ranges from 200 to 500+ hours depending on grade, so match the grade to site conditions.

The EPDM washer bonded under the hex head seals the screw hole against rain and condensation when the screw is tightened correctly. Over-tightening crushes the washer and under-tightening leaves a gap, so a screw gun with depth or torque control is recommended. The washer also separates the screw head from the sheet surface. Washers are 16 mm or 19 mm in diameter.

Screws should not pierce the vapor barrier on cold or chilled insulation, because every hole becomes a path for moisture into the insulation. On cold lines insulated with PUF Pipe Section & Board or Cellular Glass Block & Pipe, cladding is usually secured with Insulation Band & Buckles instead, or with fasteners that do not reach the barrier.

A self-tapping screw forms its own thread in a pre-drilled hole or thin material, while a self-drilling screw also has a drill point that makes the hole. The cladding screws in this catalogue have a self-drilling tip, so no pre-drilling is needed on thin cladding sheet; thicker steel supports may still need a pilot hole.

These screws are listed to DIN 7504, the standard for self-drilling screws, and ASTM F1941 for electrodeposited coatings on fasteners, which relates to the zinc-plated GI grade. Stainless steel screws are passivated. Tell us in your enquiry if you need material test certificates or a specific grade marking and we will confirm what is available.

Self-tapping screws of iron or steel fall under HS code 73181400. Both the GI and stainless steel grades are steel screws, and the destination customs authority may apply its own national sub-heading and duty rate, so your customs broker should confirm the local classification before import.

Self-tapping screws are packed in boxes of 100, 500 or 1000 pieces and quoted per size and material. Because they are small and dense, they usually travel in the same container as Aluminum Cladding Sheet & Coil, insulation and bands rather than on their own. In your enquiry, list size, material grade, washer size and quantity.