There are normally at least 4 strengths, 40% 43% 43.2% for S Africa and 42.8% for India. Normally 40 and 43 have about 97%+ of the market and the only difference is what that countries laws are. In the past the US had strengths of 80 proof, 86 proof and 86.6 proof i.e. 40%,43% and 43.3% but I never knew why.
The only difference is a drop of water, the whisky's the same