The 3D, threepence, three pennies, thrupence - slang was Trey or Tray - produced from 1910 to 1964.
1910 is a one year type of Edward VII
From 1911 to 1936 the same coat of arms was used on the Reverse and in 1938 the Reverse with 3 heads of wheat was introduced and remained until end of production in 1964.
The key to the series is the rare 1921/22 overdate which I have managed to get a friend's photo of one.
There are different obverses for Edward VII, George V, 2 for George VI (with and without IND:IMP) and 2 for Elizabeth (with and without defender of the Faith)
The Mints have included London, Melbourne, San Francisco and Denver
Starting off with old baldy we have the 1910
Obv - Edward VII

Reverse

George V type

Obv - George V


Reverse

George VI type 1

Obv - George VI - has Ind:Imp in legend


Reverse - change of Reverse from Coat of Arms to wheat stalks

George V Obverse type 2

Obv - George V IND:IMP has been removed following India's Independence



Reverse

During the Second world war threepences were produced at Melbourne and in the US at the San Francisco and Denver

Mints in 1942 and 1943.
The coins are distinguished by : no Mintmark for Melb, D for denver and S for san Francisco

These are the 1942 Threepences
Melbourne Reverse


Denver Reverse


San Francisco Reverse

The 1943 Threepences

These are the 1943 Threepences
Melbourne Reverse


Denver Reverse


San Francisco Reverse

Threepences were also produced in London in 1951 and are mint marked PL - generally the strike is much better on the coins and the planchets were better prepared

London

the next aussie buy im gunna get is three pences!!

There are two types of Elizabethe II obverses - with and without the Defender of the faith in the Legend.
1953 and 1954 do not have F:D, 55 to 64 have F:D in the top left of the legend

Without


With


Rev

Just for fun here are a few 3d errors and varieties

1917 Three legged emu


1927 Die crack Obv


1927 Die crack Rev



1942M die crack - the 1942 M is a scarce coin in any grade


1942d die crack - three legged emu

some more errors
1953 Die Clash


1960 Broadstrike Obv


1960 Broadstrike rev


1963 Misstrike obv


1963 Misstrike Rev


1963 Missing Nose - probably a worn die

ahhh all those nice lookin coins ^_^

and last but not least - the two overdates of the series 1934/33 and the extremely rare 1922/21

1922/21 Obv


1922/21 Overdate rev


1934/33 Rev


1934/33 Overdate rev detail

And a Brockage
1944s 3d - the normal reverse of a full reverse brockage coin


1944s 3d - full reverse brockage detail