All years of issue of the New Zealand Sixpence from 1933 to 1965 featured the now extinct "huia", a species of wattlebird.
The Huia featured on the reverse of all New Zealand Sixpences from 1933 to 1965 inclusive.
New Zealand Sixpences from 1947 to 1965 were made from a copper nickel alloy.
With the possible exception of traders tokens (with the traders business name on them), New Zealand has never issued a Farthing coin. Any Farthings circulating in New Zealand would have been British Farthings.
"Zack" was a slang term used mostly in Australia and New Zealand for a Sixpence. The term is thought to have originated with the Scottish pronunciation of Sixpence - being "Saxpence", with a thick Scottish accent.
A New Zealand 1954 50% silver Sixpence (George VI), uncirculated and in absolute mint condition could fetch up to $170 NZD. If it has been circulated but still in good condition, it might fetch anything from $4 to $50 NZD. There were 940,000 minted. A reputable coin dealer will be able to give a more accurate valuation.
See the links to the related questions below.
A New Zealand 1939 50% silver Sixpence (KG VI), uncirculated and in absolute mint condition could fetch up to $275 NZD. If it has been circulated but still in good condition, it might fetch anything from $3 to $75 NZD. There were 0.7 million minted. A reputable coin dealer will be able to give a more accurate valuation.
A New Zealand 1951 cupro-nickel Sixpence (George VI), uncirculated and in absolute mint condition could fetch up to $15 NZD. If it has been circulated but still in good condition, it might fetch anything from $2 to $7 NZD. There were 1.8 million minted. A reputable coin dealer will be able to give a more accurate valuation.
A New Zealand 1948 cupro-nickel Sixpence (George VI), uncirculated and in absolute mint condition could fetch up to $160 NZD. If it has been circulated but still in good condition, it might fetch anything from $2 to $50 NZD. There were 2 million minted. A reputable coin dealer will be able to give a more accurate valuation.
With the possible exception of traders tokens (with the traders business name on them), there were no "New Zealand" Threepences minted prior to 1933. Any Threepences circulating in New Zealand prior to 1933 would have been mostly British Threepences and some Australian Threepences.
All New Zealand "silver" coins from 1933 to 1946 inclusive had a 50% silver content. All New Zealand "silver" coins from 1947 onwards, were made from a copper/nickel alloy.