The square head on the adjusting screw measures 4mm across. I feel a better option is a Craftsman metric ignition wrench set. It contains a 4mm wrench along with 9 other sizes. Very nice for carb work .....
http://www.ebay.com/itm/NEW-10PC-CR...781?pt=LH_DefaultDomain_0&hash=item2c97bb45f5
http://www.ebay.com/itm/NEW-10PC-CR...781?pt=LH_DefaultDomain_0&hash=item2c97bb45f5