Here's a tool I built out of a sheet metal wrench that came with an office chair for assembly. I bought a cheap screwdriver and welded the wrench on the end. It's patterned after the tool that International uses.
Business end of the tool. Gap is 3/8-inch wide plus a little. (may need to be bigger, as I haven't tried it out yet) thickness is about 1/16-inch with a little taper on the ends. Tried the tool and had to widen the gap to 1/2". Worked well at that size.