Tippet is a length of fine fishing line that is attached to the end of the fly line and to which the fly is attached. The tippet is typically made of monofilament or fluorocarbon material and is much finer in diameter than the fly line. The purpose of the tippet is to allow the angler to make precise presentations of the fly and to help protect the fly line from wear and damage.
The size of the tippet is typically chosen based on the size of the fly being used and the size of the fish being targeted. Tippet sizes are typically measured in either pounds of breaking strength or millimeters of diameter. Smaller tippets are generally more delicate and can be more easily broken, but they also present the fly more naturally and are less likely to spook wary fish. Larger tippets are more durable but can also be more visible to the fish and may not allow for as delicate a presentation of the fly.