Use the heaviest wire that will fit easily through the beads. For example, a bracelet, which as it is worn on the wrist and always in motion, use the strongest material. Try always double-crimping the wires for additional security, and pass the wire through reinforcements so the wire covering will not chafe on the clasp and wear down. With a short necklace you can use thinner wires or thread, because there is little chance it will catch on something heavy. With a longer necklace, use something strong. You also want to consider a match between beads and stringing material in that if the holes are large and the string is thin, the beads may hang crookedly. Having the hole filled or nearly filled with stringing material allows for greater evenness.