Most roofing leaks and rust streaks on PEB sheds start with the wrong screw, not the wrong sheet. This guide explains how to choose self drilling screws for metal roofing and cladding: the coating, the size, the Tek (drill point), the length and the washer. It comes from our team at Fasteners King, authorised Corroshield distributor, supplying PEB builders from Delhi and Guwahati.
- Outdoors, never use plain zinc-plated screws – choose a corrosion-resistant coating such as Ruspert or Xylan (Corroshield).
- Match the Tek (drill point) to the steel thickness of the purlin.
- Pick a length that passes through the sheet, any insulation and the purlin, with the threads fully engaged.
- Use a bonded washer wherever water can seep in.
1. Choose a coating made for outdoor roofing
Zinc-plated screws are made for dry, indoor use. On a roof they meet rain, condensation and industrial air, so the coating breaks down, the screw rusts and red streaks run down the sheet. For roofing and cladding, choose screws with a corrosion-resistant coating such as Ruspert or Xylan. Corroshield self drilling screws carry a Xylan coating.
2. Choose the right screw size (gauge)
The first number in a size like 12 x 25 is the gauge (diameter) and the second is the length in mm. Common roofing gauges are:
- 10 gauge – about 4.8 mm
- 12 gauge – about 5.5 mm (the most common for PEB roofing)
- 14 gauge – about 6.3 mm
3. Match the Tek (drill point) to the steel thickness
The Tek number tells you how thick a steel section the drill point can drill through – the higher the number, the thicker the steel. If the Tek is too small for the purlin, the point overheats and stops drilling; if it is far too big for thin steel, the screw may not hold well. Always check the thickness of the purlin or steel section before you order, and tell us – we will match the Tek for you.
4. Pick the right length
Add up the total thickness you are fixing through: the sheet, any insulation or profile height (for crest fixing) and the purlin. The screw must pass through all of it so the drill point clears the steel and the threads are fully engaged. Too short and the screw will not hold; too long and it wastes material and can loosen.
5. Thread type
- Full thread (FT) – short sizes such as 12 x 25 and 12 x 35, used for everyday sheet-to-purlin fixing.
- Double thread (DS) – longer sizes from 12 x 45 to 12 x 100, for thicker build-ups.
- Fine thread – 12-24 sizes, generally used on heavier steel sections.
Not sure which one your job needs? Send a photo or drawing of the roof detail on WhatsApp and our team will recommend the size.
6. When to use a bonded washer
Use a bonded washer wherever there is a chance of water seepage – most roofing and exposed cladding fixings. We stock 19 mm aluminium bonded washers for Corroshield screws.
3 common mistakes we see
- Buying zinc-plated screws for outdoor roofing instead of Ruspert- or Xylan-coated screws.
- Buying the wrong length or head size for the sheet and purlin.
- Buying the wrong Tek size for the steel thickness.
Our fastest-selling Corroshield sizes
| Size | Type | Delhi price per pc (GST extra) |
|---|---|---|
| 12 x 25 | Full thread | ₹4.13 |
| 12 x 35 | Full thread | ₹4.95 |
| 12 x 55 | Double thread | ₹6.82 |
Indicative Delhi prices per piece, GST extra. Prices may change without prior notice – WhatsApp for today’s best price. See all sizes: Corroshield screws in Delhi · Corroshield screws in Guwahati.
Trusted on major projects
Fasteners King has supplied fasteners to large projects including Jewar Airport and the Tata semiconductor project in Assam.
Frequently asked questions
Can I use zinc-plated self drilling screws on a roof?
Not recommended. Zinc plating is for dry, indoor use. Outdoors, choose a corrosion-resistant coating such as Ruspert or Xylan.
Which screw size is most used for PEB roofing?
At our branches, 12 x 25, 12 x 35 and 12 x 55 are the most popular sizes with PEB builders. The right size for your job depends on the sheet, insulation and purlin thickness.
Do I need a washer with roofing screws?
Yes, wherever water can seep in. A bonded washer seals the hole around the screw.
Do you supply in bulk for projects?
Yes. Send your BOQ or quantities on WhatsApp for a project rate. We dispatch within 24 hours of PO, subject to stock, from Delhi and Guwahati.