spanner wrench for castellated steering stem nut

[markmartin]

Does anyone know what size spanner wrench is needed for the steering stem nuts?  I'm having a little difficulty finding an adjustable one locally.  The outside diameter of the nut is about 1.570" / 40mm.  I found a couple of yamaha part numbers for spanner wrenches, but sizes were not indicated, nor were applications.

Or if there is another tool that could be used to work these castellated nuts? I need to adjust the steering stem as I'm getting a slight knocking.

Questions about steering stem adjustments to follow...:-)

[yampug]

big screwdriver plus hammer.