Because the Suzuki Gsxr 600 and Gsxr 750 engines shared a lot of parts, Suzuki moto had to find ways of reducing weight on the Gsxr 600.
With less power than the Gsxr 750, certain stresses were lower on the Gsxr 600, so the engineers could lighten some parts.
One solution was to use tapered bolts holding the crankcase modules together.