Fettling to Driving Ratio?

[Reckless Rat]

That it be, but a "Fettler" is someone who works in a foundry and is charged with removing the sand from a casting after it has cooled and been taken from its mould and preparing it for the hands of the machinist. Hence the term for something nice and clean being "in fine fettle". Now on a slightly similar note, a neighbour of mine in a former life was an accountant at Dyson's refractory works in the Loxley Valley (DW will know the place). They used to make "saggers" among other things from refractory clay, which were used in the firing process, from whence came the employment of someone to check the soundness of the sagger before it was used in the furnace. The tool they used was called a sagger maker's bottom knocker. (from "What's my Line")

Saggers were particularly useful for growing tomatoes...