Looking for the name of a screwdriver type - for tightening nut on 3.5mm audio jack

Hi

I hope this is the right group to post this question, apologies if it isn't.

I'm using some of these panel mount 3.5mm audio jacks for a project http://uk.farnell.com/lumberg/klb-4/socket-3-5mm-jack-chassis/dp/1200144

The holding nut has two dimples (for want of a better term) that I assume you use a special type of screwdriver or wrench to tighten but I haven't a clue what it's called so don't know where to start looking.

I thought I was on to something with a pin wrench but they don't seem to go down to that size.

Thanks

Tommy