OSX 10.9 - Two finger click for middle click?
BetterTouchTool does not support two finger tap/click actions. There was an experimental version a long time ago but it was implemented in a 'hacky' way and never really worked right.

BetterTouchTool does let you set up a TipTap to middle click, so that you can press with a second finger whilst your first is down (sort of like a two finger click but with a delay) to activate a middle click:

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Alternatively, you can set up a tap/press with three fingers to middle click in BetterTouchTool. This is supported fine:



If you're really looking for a two-finger click, KeyRemap4MacBook lets you remap right click to middle click using a private.xml such as this:

&lt;?xml version="1.0"?&gt;
&lt;root&gt;
  &lt;item&gt;
    &lt;name&gt;Right Click to Middle Click&lt;/name&gt;
    &lt;identifier&gt;remapRightClickToMiddleClick&lt;/identifier&gt;
    &lt;autogen&gt;
      —PointingButtonToPointingButton—
      PointingButton::RIGHT, PointingButton::MIDDLE
    &lt;/autogen&gt;
  &lt;/item&gt;
&lt;/root&gt;


See private.xml documentation for more information and to limit to certain apps.