basically the nut that the arrow's pointed to has fallen off, it's the one round the other side of the bolt that you can see with the hex key head. This doesn't mean the caliper doesn't work, but it does make it slightly skewift, as in one of the brake blocks is slightly ahead of the other on the rim. Also you can move one of the caliper arms in relation to the other a little bit whereas on my front one you can't. I ordered a new tektro one off CRC but they sent me a brake lever instead, the numpties. I phoned them up to complain but they said they've got the tektro calipers in stock but can't find them because they must have been labelled wrong, so can't send me one. Great. (I've since sent them an email to complain because that's two out of my last three orders that have been wrong, but that's another issue...) I've asked in the LBS if they've got a spare nut that would fit but they didn't. Now I can't decide whether to get a whole new caliper or not and if so which one to get I don't know whether it is one, but my current one looks remarkably similar to the shimano tiagra in the picture. I don't want to spend too much but don't want the same thing to happen again! I don't know why the nut fell off, I don't even know when it happened but basically I just noticed that the bolt had worked itself loose and the nut had thus obviously fell off. The front one is fine, the bolt's fully in and the nut is still there on the back. So I want people's opinion on whether i should (a) get a new back brake (advantages: could do with new blocks anyway as had to chop the wilko's ones down and there is a bit of metal showing which I don't like, peace of mind - disadvantages: cost, don't like replacing parts unless necessary) ( hunt around for another nut (advantages, secure fix and will hardly cost anything, disadvantages: time consuming and possibly fruitless hunt) (c) sod it (advantages: easier, might not be necessary anyway, disadvantages: niggling doubt that it might fall apart even though it is unlikely. help me decide people please...thanks!