Do you know.. when did cricket mandate to have a six ball over?

Test cricket started with 4 balls per over with the standard finally changed for all in 1979/80.

England went to 6 in 1946, Australia went to 6 then 8 and back to since in 1979.

South Africa in 1961/2, and everyone else to 6 in 1979/80.

Interesting!