As useful as ........................

..... screen windows on a submarine.
......a wheel on a crutch.
......an ashtray on a motorcycle
......a one armed wallpaper hanger.
......a one-legged tightrope walker.
......a chocolate teapot.
......a hat full of arseholes.
..... tits on a bull.
..... a three dollar note
..... an ejection seat in a helicopter.
..... a map of the Sahara.
..... a wet towel.
..... a sundial in a mineshaft.
..... a Volkswagen radiator.
..... a bicycle to a fish.
..... a toothbrush to a turtledove.

I couldn't find a collation of these, so decided to do it myself. Additions welcome.