Gives a few extra inches to the girth strap of DT Harness, DT Harness with Chest Support, DT Guide Light, & DT Universal models. This extender is great for still-growing puppies and mature canines that are between sizes. Extensions for harnesses sized Small - X-Large measure 5" in length and feature a black buckle with one red button; extensions for XX-Small and X-Small harnesses will measure 4" in length and feature an all black buckle. Extensions are meant to be used with Dean & Tyler products. It is not recommended to attempt use with products from another brand as compatibility is unlikely.