Bonsai wire is available from 1.0 mm which you would use to wire the smallest and most delicate foliage to 4.5 MM which serves to bend large branches and even some trunks.
This is bronze anodized aluminum wire available by size or as a set.
1.0, 1.5, and 2.0 MM rolls are approx 25 feet of wire
2.5 and 3.0 MM rolls are approximately 15 feet
3.5, 4.0 and 4.5 MM rolls are approximately 10 ft
Best price is to buy the set with 1 roll of each size for $30.00