In the UK, the suffix numbers in bulb shapes are the measurement in millimetres at the widest part of the glass. A standard 100 watt lamp would be PS60 - P (pear), S (straight section at the neck), 60 (60mm at the widest point).
To confuse things, Americans do things differently. The system in use Stateside is to measure the widest part in 8ths of an inch. So the standard US 100 watt lamp would be A19 - A (Arbitrary - continuous curved shape), 19 (19 8ths of an inch).
And no matter where in the world you are, reflector lamps get measured in 8ths of an inch always. So the standard 12 volt halogen spot lamp is a MR16 - M (mirrored), R (you get the idea...)
There may be exceptions of course, but nothing jumps out at me right now.