These filaments are used in the pullers. The filament is the platinum iridium metal component that heats up to warm the glass as you pull it. As it heats, it expands a little, and it contracts when it cools. Over time, the expansion and contractions tends to wear down the filament. Eventually, a filament wears out and must be replaced. The shape of the filaments you choose is a matter of preference, depending on the end result of the pippette you wish to create.