This pack includes 100 3mm diameter rare earth magnets, suitable for use with Bat Bases. 100 magnets is approximately enough to complete 3 or more packs of 15cm grid bases:

• Skirmish unit packs require 30 magnets
• Standard unit packs require 24 magnets
• Deep unit packs require 27 magnets
• Base/camp packs require 18 magnets

You'll find a piece about how to fit the magnets, here.