Exactly that. The hooks locate the top bottom and sides of each slate, and each slate is retained top and bottom. One hook to fix per slate. They're black finished stainless steel.
Well I never knew that.... When you use hooks you can use unpunched slates, or just leave the holes - they are not needed (1st courses, verges etc still have to be nailed). The battens are SIG roofing 25 x 50 https://www.sigroofing.co.uk/timber/
All slates have mineral inclusions. Some are non rusting .
In this case , it does mean possibly a low grade slate.
Batten colour does not indicate batten quality .
Natural slate on batten one would used 25x50 up to 600 rafter spacing.
On the sea front in the south we have hooked and nailed natural slate to avoid storm damage
If it's new build and you are buying off the builder, I would be sending those images to their marketing team and telling them you'll be posting them on their social media pages if they don't re-do the roof. That's just awful.
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