David,
Pole floats that take less than about 0.75 grams shot load are often marked in Styl lead weights not shot. If you see 4 x 18, 4 x 16, 4 x 14, - very small floats 4 x 8 this will usually refer to Styl leads which are different to lead shot weights.
Styl leads are a bit like Stotz but in bigger sizes and generally only available in the very small sizes in the UK as the bigger szes are illegal in lead. These float markings are following the Continental convention. There are some UK made floats that have shot weights on them or gram sizes.
Shot weights are no 8 = 0.06 grams, No 6 = 0.10 grams.
Styl weights are:
no 20 = 0.258
no 18 = 0.170
no 16 = 0.13
no 14 = 0.08
no 12 = 0.05
no 10 = 0.03
no 8 = 0.015
So a pole float taking 4 x 18 = 4 x 0.17 = 0.68 grams = 11 x no 8 shot or a 0.50 gram Olivette plus droppers.