Which cable needles?

Cable needles seem to come in packs of two, with one needle finer than the other. Which is used for which weights of yarn? I’ve also seen needles with kinks in them – what are they for?
Rita Peters, Macclesfield

The finer needle is used for double knitting and finer weights of yarn, and the thicker one for aran weights and thicker yarns. The needles with kinks in them are simply a variation on the straight ones, which some people find helpful as the stitches are less likely to slip off. The main consideration is that the stitches placed on the needle should be sufficiently secure so the needle does not slip out.