Shift Knob Set Screw Size?

I did a search but only seemed to find discussions of shift knob replacements.

The stock shift knob on my 2005 Federal Elise is getting a bit loose. I think the fix is as easy as tightening the set screw at the front of the shift knob.

I don't have a tool set, so I'll need to buy the proper tool for the job. Does anyone know exactly what size I need? I didn't get a close look at it, but I assume it's a hex screw?

I'd rather not buy a whole set of allen wrenches if I can just get away with buying a single one to get this job done.