Product Description The " clears" the chain when the rear wheel is missing. This way it does not dangle around when driving screws. Specifications:Material:steelDimensions:85 x 40 x 11 mmManufacturer Number:BM17-CHAIN-KEEPER Contents:1 x Manufacturer: Birzman No. 8 Gongye 1st Rd. Dali Dist. Taichung City 412 Taiwan info@birzman.com Distributor: Sports Nut GmbH Au-Ost 3/1 72072 Tübingen Germany contact@sports-nut.de