One pack weighs ~1.8g. Thats about 130 to 140 pieces of crimp beads
Outer diameter: ~2mm
Inner diameter: ~1.1 to ~1.2mm
Recommended for jewelry wire thicknesses between 0.3mm and a maximum of 0.60mm
Material: Brass with a high-quality, silver color electroplating (nickel, lead and cadmium 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.