About 75 crimps.
Crimp tubes are how to finish the end of a beading wire and attach a clasp. Slide the crimp tube on after the last bead, add a jumpring or the loop of the clasp directly, then go back through the crimp tube with the beading wire. Crush the tube flat with your pliers, or better, use crimp pliers to crimp and fold the crimp into a nice, secure completed crimp.
2mm By the pack of 1.5 grams.