In fact, I recently mounted an ATV 29 "singlespeed from scratch and I got stuck with my rear wheel axle thin quick coupler and wide rear horizontal dropouts my part: the wheel could not be firmly fixed without rip to the first shock. Not to mention hell align the wheel with a correctly tensioned chain.
This "tuggnut" is simple but brilliant. The machine incorporates a screw thread (behind the "s" that you see in the picture) through which the threaded rod that pushes you see a moving piece which itself is wedged on the end of the horizontal leg rear of the frame. As the wheel axle is fixed to the "tuggnut" (even with shaft end wheel quick-passing in the joined adapter - the puck in the picture), this will gradually pull the wheel axle to the rear of the bike without any effort (*) and thus tighten the chain properly (too much or not enough). View on Google images if my explanations are incomprehensible ... A "tuggnut" on each side of the bike would surely better but only the transmission side (where is the voltage) is enough already very good.
Bizarre it has little competition in the market and that Chinese factory does not produce an equivalent product for a tenth of the price ... I have found that this ersatz beautiful store "Saddle Marcel "in Paris (a Japanese MKS brand chain tensioner without taste or flavor and almost at the same price). But the "tuggnut" Surly is undoubtedly the most fun!
(*) NB: screw and completely unscrew the threaded rod once before mounting it turns without difficulty once the "tuggnut" mounted. There are in fact originally a dose excessive in my opinion blue thread lock on the threaded rod. Ideally, it could be screwed with an Allen key rather than by hand elsewhere. But on the other hand, fewer tools to use best?