Early small 5p pieces have a different edge...

[mint_mark]

...don't they?

I've been looking at small 5p coins and I've noticed that in 1990 and 1991 the coins have a more rounded edge. That is, if you look from the side the corners are not as sharp. Looking at the rased ridges of the graining pattern, it looks like they have been shaped at 45 degrees across the edge of the coin.

On coins 1992 and later the graining extends all the way across the edge and the corner is much more like a right angle, making the coins feel sharper around the edge.

I don't know what they changed... it makes it look like the later coins are thicker, but I don't think they are. Similarly, I don't imagine they contain more metal either as that could change the weight. Perhaps they are struck with greater force?

Does anybody know any more?

[Sylvester]

Some 1992s are the old 'wire edge' variety too i believe. Many, many things changed in 1992. The 20p effigy, the bronze coins were changed to copper plated steel, the new 10p coins, of which they do exhibit the same 'wire' and 'flat' milling variants for 1992.

The coins are the same size and weight the only difference is the edges are camphered and make the edges look thinner.

Why did they change them? Well personally i prefer the flat edge varieties and i presume vending machines prefer them too.