What are these ?

[Rewound]

In a recent garage clearance we come across quite a lot of these in different sizes, some sort of rivet of fastening, maybe ?

may be some sort of crimp to tidy up the ends of frayed cables ?

 

[Steliz]

I don't know but if you were making a bong these would be ideal.

 

[flying haggis]

My first thought was decorative covers for tyre valve stems, but your suggestion of ferrules for wire rope ends sounds good.
https://velotastic.co.uk/product/parts_and_accessories/stopping/10-off-inner-cable-ends/these are for bicycle brake cables to stop the end fraying so perhaps your ones are for similiar

 

[ajs]

In a recent garage clearance we come across quite a lot of these in different sizes, some sort of rivet of fastening, maybe ?

may be some sort of crimp to tidy up the ends of frayed cables ?

Yup. Uninsulated bootlace ferrules. Used on cable ends to bind the strands together. Tinning with solder is the other alternative but soldered ends are a no-no with screw terminals since the solder can flow under pressure over time.

 

[flying haggis]

Not seen uninsulated bootlace ferrules with such a large " cup"