[Closed] Tighten up the back brakes on a Brompton M3R

Hello,

Can anyone advise how to tighten the back brakes on an M3R? The front brakes have a screw that moves the brakes closer to the rim, but on the back is not clear.

The central screw thing does not seem to move the brakes closer to the rim.

I've attached some photos.

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[url= http://s14.postimg.org/hwtf3azwd/IMG_20150615_151409.jp g" target="_blank">http://s14.postimg.org/hwtf3azwd/IMG_20150615_151409.jp g"/> [/img][/url]

Thanks!
Alex