What are these screws?

[Noyade]

I 'found' these recently. FHD screws?

Through wood then self tapping into sheet metal?

Need a pilot hole?

Similar? 

[EricL]

Hi @Noyade 

They look very similar to the Zenith 8G x 40mm Galvanised Countersunk Ribbed Head Winged Screws - 18 Pack. These are usually used for mounting timber to steel applications.

Eric

[Noyade]

Yes they do - thanks @EricL 

My screws are at least 40 years old - and I was wondering if age affects metallurgy?

There was no way I could self-tap though 2mm steel plate - as you can see above the tip wore down to a wood twist drill profile, with no penetration.

In the end I resorted to pilot holes - the best being 3.5 mm diameter - even then, I noticed a couple of the 'armoured' cutting tips had shattered off on one side...

[EricL]

Hi @Noyade 

I suspect that these screws are for light duty only. If it ever came up to something serious it would probably split or crack.

Eric

[Noyade]

All good in the end @EricL 

I managed to attach a 'safety' steel mesh screen to the fence, to hopefully protect my neighbour - particularly when angle grinding.

.

Cheers.