How do I fit this pair of chain tensioners on my single speed bike?
They look like you want those "in" the horizontal dropout. The bracket should cover the frame and as you tighten the bolt it will pull the axle further away from the cranks, tightening the chain along with it.



Be careful to not over tighten as you want a little 'slack' in the chain. Also, it is very easy to tighten one side more than the other resulting in your wheel not rolling straight (just slightly off center is what I see most often).