The most common types of screws are Zinc plated steel, Zinc-aluminum alloy and Stainless Steel.
- Stainless is used primarily for long-lasting applications, due to its corrosion-resistant nature and durability.
- ZC-Alum alloy (ZAC) is an excellent choice for GALVALUME & other long-life metal roof panels
- Zinc screws are a more cost-efficient route. Though they may be less expensive, they are still resistant to corrosion and durable.
|Stainless Steel Cap Screws||ZAC Cap Screws||Zinc Cap Screws|
|304 ¼” stainless caps, which provides lifetime warranty against red rust on the head & washer
|5/16” large cupped Zinc-aluminum cap||¼” Zinc-plated steel V-neck cap||Rubber washer beneath cap for a water-tite seal|
|Scratching/ burring will not create surface rust since corrosion resistance exists within the metal itself
|provides lifetime protection against red rust on the head & washer||If scratched or burred, rust may occur||Micro-Bit point, which reduces metal shavings that can embed themselves in the rubber washer and is fully threaded to the end and is designed for the quickest penetration through light gauge steel panels.|
|The smaller cupped HWH provides an attractive low-profile appearance versus larger HWH fasteners.
|Threads transition from fine to coarse||Threads transition from fine to coarse||Self-tapping (no need to pre-drill holes)|
|Used in marine environment
|Will rust in marine environment|
Pullout & Pullover & Why test for this?
Screws are tested for their performance in different applications; mainly for strength values known as pullout1 and pullover2. Testing for this is important because it demonstrates how many pounds per square inch the screw can withstand, before it begins to come out of the embed it is in, while the metal it is anchoring down is being pulled on.
The results show which screws hold better in different types of wood being used to test with and which wood gives the screw a better hold in such uplift situations; the lesser the value has to do with the density of the wood.
Proper tools = proper washer seal
Apply enough torque to seat the washer – do not overdrive the fastener. An impact tool will over or under compress the seal of the washer, causing the screw to leak.
1 pullout- screw loses its grip
2 pullover- the material around the screw fractures