One pack weighs ~3.9g. Thats about 140 to 180 pieces of crimp beads
Outer diameter: ~2.5mm
Inner diameter: ~1.5 to ~1.6mm
Recommended for jewelry wire thicknesses up to a maximum of 0.8mm
Material: Brass with a light gold 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.