Delicas are very tiny sliced tubes, and are somewhat like working with blocks, instead of balls.  
In older pattern books, instructions tell you to use Delica Beads.    Because there are so many brands of similar beads today, 
newer pattern books tell you to use Cylinder Beads, which is a generic term.

11/0 Delicas are 1.8mm in size.   These are sold in 10 gram tubes,(though some more expensive colors are in 5 grams tubes -- the order sheets specify the amount of grams in the tube).

There are approximately 1900 delica beads in a 10 gram tube.