It may be of interest to North Americans that Governor Macquarie copied the idea of making "holey dollars" from elsewhere: Governor Charles Smith of Prince Edward Island, Canada, issued a similar series of punched-out and countermarked dollars and dumps, for a similar reason: to combat the export of coins by mutilating them, thus making them unacceptable to merchants outside of the colony. In both cases, the coins were also given inflated values, making the colony that issued them the only place the merchants could obtain "full face value".
The PEI dollars and dump were cruder affairs, with a simple circle-of-triangles countermark;
Here's an example of a dollar. As a result, they were relatively easy to counterfiet, such that today it's impossible to tell the difference between an "official" PEI holey dollar and a contemporary counterfeit.
Governor Macquarie down in New South Wales presumably heard of both the concept of a "holey dollar" and the difficulties with private imitations, so he took steps to make his coins a bit less reproducible, by stamping a ring around the hole left in the dollar, and by grinding flat and overstriking the dumps.
Because the former were simple countermarks, a PEI dump should fit neatly inside a PEI dollar. But because the inner rim of the NSW dollar was squashed down and the dump flattened by counterstriking, a NSW dump is much larger than the hole in a NSW dollar.
In 1988, the Perth Mint began issuing a series of .999 fine silver proof "bullion" coins with a "Holey Dollar and Dump" design and an aboriginal theme. The "Dollars" are $1 face value and 1 ounce, the "Dumps" are 25¢ face value (Australia's only "quarters"!) and 1/4 ounce of silver. The sizes were made to match; the "Dump" will fit exactly inside the hole in a "Dollar".
The Perth Mint issued "Holey Dollar and Dump" pairs in 1988, 1989 and finally in 1990, when the series was halted. The 1988 ones, sold as bicentennial souvenirs, are the most common. Finally, a Centenary of Federation "dollar and dump" was also made in 2001, with the "dump" star-shaped.