What fasteners for old corrugated cement board garage roof?

[-Alan-]

Hi,
I have a flat garage roof with corrugated cement board (including asbestos) sheets. The original nails have curved washers on them about 30mm diameter that are disintegrating due to age and the nails are working themselves out, they are nailed into wooden purlins.
What would be suitable screw fixings to replace these with?
I've looked at Screwfix part 5672P but the washer is only 16mm, would this be suitable?
I've not been able to find any similar curved washers like the originals, probably because I don't know the real name for them.
Any advice appreciated.

Alan.

 

[Tigercubrider]

me neither but can I suggest screwing the sheets down? (assuming the nails can come out?)
less dust than banging nails.

Are the washers curved when new?

 

[-Alan-]

Hi,
I'll definitely be using screws but just wasn't sure what's best, I was thinking if these.
https://www.screwfix.com/p/easydrive-roofing-screws-6-3-x-80mm-100-pack/5672p

I'm assuming they were shaped for the roof but it's hard to tell from what's left.

 

[pcaouolte]

The washers are not curved when new but they are flexible. See here for examples: https://timco.co.uk/19631-dowty-type-washer

 

[lostinthelight]

More the type you need:
https://www.roofingsuperstore.co.uk...MIkNeRjbGI8gIV5IFQBh0f9w7VEAQYBSABEgJXcPD_BwE

They have another set of larger diameter threads under the head, the ones op linked are sheet metal

 

[-Alan-]

Thanks, found something similar to those that should work.

More the type you need:
https://www.roofingsuperstore.co.uk...MIkNeRjbGI8gIV5IFQBh0f9w7VEAQYBSABEgJXcPD_BwE
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