Each pack contains 1.8 gram (~130 pieces) crimp beads.
Diameter: 2mm
Material: brass with black lacquer / nickle-free

Crimp beads are primarily used to secure clasps to beading wire (nylon-coated steel wire). They are easily compressed with fine, smooth flat-nose pliers. Crimp beads can also be used with beading wire as stoppers for evenly spaced necklace designs.

A tutorial for attaching clasps with crimp beads you can find here.