The size rope is 6.5 mm wide marine rope bought from a Ships Chandler.
For a larger knot use a thicker rope or use four loops instead of three.

What is was originally used for before it became a dogs tuggy.

The Monkey Fist is used as an end knot for a heaving line. A heaving line is a line used for throwing from one location to another. This enables a larger line that could not be thrown over the distance to be pulled over.

The most common use of a heaving line is at sea, to pull a cable to shore from a ship. A cable is not easily thrown over a distance of 10m [ ft]or more, so instead one throws a heaving line. The line is tied to the cable and when it has been received the cable can then be pulled over.

To make it easier to throw one needs to connect a weight on the end of the line - usually a stone, lead-ball or a small bag of sand is connected to the end. Better still a small rope ball is tied on the end. It is neat, it will endure many tosses last long and it is easily thrown. That is what the monkey fist is was originally used for.

The knot can be done with or without a central core (i.e. a round stone or ball bearing) to add extra weight but it is recommended to use extra loops depending on the size of the object.