DilweAluminium Bike Chain Tensioner, Single Speed Adjuster, Black & Red, 63g, Folding Bike 11T/13T Derailleur

Such an appalling product, teeth on the wheel aren’t even big enough to grasp the chain so just kept sliding off, spent more time putting the chain on than riding, the hole that you use to attach to bike doesn’t have any thread and isn’t the same size as a bolt so moves around when attached to chain, all in all your better off spending your money elsewhere this product is appalling and has been returned due to its poor quality

Lasted a while but inevitably broke - as these all do!

Price is ridiculously high for a part not useful without buying extra components... do not buy, take another option, there are plenty.