MKS Track Bike Chain Tensioners - NJS (Allen)
[311-101-13]

These are indispensable if you ride a fixed/single speed bike. Really worry free riding, your chain will never slacken! Plus it is the best way to tension your chain and then tighten down the axel nut (notice that without the MKS, the nut tightens toward the chainring which always loosens it)I feel much better riding now with the MKS on my bike! Great product and highly recommended! (I took some foto's but I cannot paste it on this review)