Use professional grade kettlebells.
They are made from steel, not iron, have a consistent size throughout the range of weights and a thinner handle.
The exposed steel on the handle should be lightly sanded to rough it up, then covered with chalk. Then, chalk your hands and you should be good to go.
That is how it is done by the professional KB lifters.
If you don't have professional grade kettlebells, they are worth the investment if you use them a lot, otherwise just follow what the others have said.