Season 1-2 and Season 3-4 differences

What are the differences between the Season 1-2 sonic screwdriver and the Season 3-4 version?

The original season 1-2 props were notoriously brittle, badly designed and assembled. Towards the end of Season 2 the decision was taken to redesign and remake the props in metal.

This redesign solved many of the problems of the first props and meant that the sonic screwdriver underwent several subtle cosmetic changes depending on who actually made the prop meaning no two props were identical. The changes encompassed mainly the colour, the slider assembly and the ridge shape.