Simple Boilies are just pastes laced with eggs, rolled into balls then boiled, this puts on a shell like outer layer which stops small fish nibbling the bait away.
Mainly used by Carp anglers used as both an attractor and a hook bait.
As a hook bait they are normally fished on a hair rig using a minimum hook size of 10.As you would expect the tackle shops stock a large variety of commercially made boilies in various flavours, colors and size, very handy when you have no time to make your own.
Making them yourself is half the fun, trying different mixtures and flavours and turning the kitchen into something resembling Dr. Jekyls laboratory .
If you must have them all the same size, there are plenty of mould's available enabling you to churn out lots of different sizes.