The butt of the leader is the thickest and strongest part of the leader. Its function is to attach to the fly line and give strength to the leader. The middle section is called the body. It tapers down to the tippet, and aids in a soft presentation of the fly. The final 18 to 24 inch section of leader is called the tippet, which is attached directly to the fly.
Tippet materials come in nine different sizes.
They all are classified with an X code according to the diameter of the tippet. The X codes range from 8X, with a .003 diameter, to a 0X with a .011 diameter. Tippit diameter remains consistant from manufacturers. Pound test is approximate and will vary from manufacturer to manufacturer. Fluorocarbon tippits do not follow above diameters.