Threepence - Transition from Silver to Nickel-Brass in 1937

The threepence represented 1/80th of a Pound. Before decimal day in 1971 there were 240 pence in One Pound Sterling. Crazy! I thought decimal day just meant we put decimal points everywhere. Yep I really am still uneducated on coins.

What I really wanted to look at was the transition from silver to nickel-brass in 1937.

The reign of King George V (1910-1936) featured several changes to the threepence:
In 1920 the metal content went from 92% silver to 50% silver, 40% copper and 10% nickel.
In 1922 the metal content went to 50% silver 50% copper.
In 1927 the metal content went to 50% silver, 40% copper, 5% nickel, 5% zinc.

George why did you change it so much?!

The nickel-brass threepence took over the bulk of the production of the denomination being produced in all years between 1937-1967, except 1947. The metal content went to 79% copper, 20% zinc, 1% nickel. WHY BOTHER WITH 1% OF NICKEL?! I need to research this at a further date!

Comparison: Here's two of my threepences. Whoever bent the silver one, I am not impressed! 

On the left has 50% silver, 40% copper and 10% nickel.

On the right has 79% copper, 20% zinc and 1% nickel.