Peculiar screws

[2192]

Does anyone know what these peculiar screws are? (See attachment.) I found about 8, new and unused, scattered along about 100 metres of pavement near where I live in Derby. I guess someone had a hole in their toolbag. They look like an ordinary screw that ends with a crude masonry bit. However if so, the hole drilled will be too big for the screw, and if a rawlplug is inserted in the hole, the screw ending will prevent the screw going in. The head of the screw is countersunk, but the hole in the centre is square, (not an Allan key hexagon, nor crosspoint). If a special tool is needed for insertion, how does anyone else get them out? And who would use them?

 

[tomuk]

They are for fixing wood to steel framing

 

[Ediswan]

This shows how they work:

Unusual screw heads are usually for security, to make it harder for others to remove them.

 

[stuartl]

The head looks like a Robertson Square one, as it allows high torque to be applied.

 

[dmncf]

This shows how they work:

Unusual screw heads are usually for security, to make it harder for others to remove them.

The requirement to have a length of exposed screw tip sticking out is a bit could be painful!

 

[najaB]

The requirement to have a length of exposed screw tip sticking out is a bit could be painful!

That'll normally be on the inside of the fitting, if you're attaching wooden siding or similar to a metal frame. The tip would be buried in among the insulation.

 

[Busaholic]

A lot of people seem attracted to this thread, not only members!

 

[2192]

Thanks everyone. I see from watching the video that the self drilling screw having drilled the larger hole in the wood, and a smaller hole in the steel, the steel makes the wing tips on the screw shear off, allowing the first screw threads to cut threads in the metal, which permits the remainder of the screw to grip.