A lip strap is a piece of horse tack used sometimes on some types of curb bit and Pelham bits. The lip strap runs between the bit shank lever arms (see Lever#Curb bit) and passes through a special center ring on a curb chain (not all curb chains are designed for use with a lip strap). The lip strap attaches to rings at midpoint of the lever arms and buckles on the near side.
The lip strap helps keep a "mouthy" horse from mouthing or "lipping" the shank. It also helps prevent the curb chain from unfastening or otherwise moving too much.
The leather attachments that are sometimes used to connect the rings of snaffle bit are also occasionally known as lip straps.