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This is the bicycle that I own:

enter image description here

My problem is that the handlebars have become loose right right where that red bolt is located. There is an identical bolt on the other side. I have tried adjusting them but they won't budge.

Does anybody know what these kind of handlebars are called and how they can be adjusted?

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    Probably unrelated to your question, but what happened to the front mudguard/fender? Looks like something was swept around by the spokes, hit the support rods, drive the fender into the tyre which completed the destruction. – Criggie Aug 24 '16 at 19:58
  • Also unrelated - chain could use some lube. – mattnz Aug 25 '16 at 0:46
  • bicycles.stackexchange.com/questions/30975/… has photos of a stem like that dismantled which may help you understand what's going on. The short answer is that adjustable stems are inherently wobbly, the best you can hope for is that the looseness isn't too bad. To get rid of it you really need a fixed-position stem. – Móż Aug 28 '16 at 23:04
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I have two bikes with this kind of adjustable stem for handlebar. It is using a simple "tooth" that hold it on position. If it is not tightened properly, the tooth will be grinded down and become lose after sometime(that cause the wobble).

To check it out, you need two wrench(with hex bits) or hex key. Wrench with hex bit is recommended, because it gave you enough torque to twist open the screw. One side turning at opposite direction while another holding the screw from turning.

After you loosen the joined screw, you will know what I mean. Now adjust the handlebar and make it "locked" properly, then tighten the screw. Make sure you make it very tight (I don't have an expensive torque wrench to measure the torque) when you place the screw back.

(UPDATE) The funny part of these kind of adjustable stem, is the "lawyer notes sticker" mentioned in Sheldon brown hands up article. Both of my bike come with this sticker. I have better quality adjustable stem on my touring bike, which you don't need much force to tighten the screw and only one hex key is required to adjust the stem.

Simple adjustable stem (Photo borrow from Sheldon Brown website, http://www.sheldonbrown.com/handsup.html )

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    The other option is to go to a fixed stem. – Batman Aug 24 '16 at 18:53
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    "Very Tight" may not be the answer. Instead a vibration resistor or threadlocker fluid may be required to help hold the bolt from backing out. – Criggie Aug 24 '16 at 19:56

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