A ferrule is a small electrical connector that comes in a variety of different sizes that is very handy when connecting electrical wires. The metal needle of the ferrule is hollow allowing you to fit the correctly sized wire for maximum connectivity and faithful conductivity.
Once well into building a simulator, the connection of wires to interface cards, power supplies, terminal blocks, etc becomes common place. Having a method to easily secure wires that ensures reliability is a great asset.
Whilst you can solder wires to the above items it is often necessary to remove a wire for testing purposes or to add an additional function to the connection. Twisting and clamping the wire beneath the screws or screw tab while functional, is far from tidy and eventually the wire will become damaged with loose wire strands.
Loose and damaged wires can translate to poor connectivity leading to frustration when something does not work correctly.
A ferrule can easily be attached to the end of a small wire (22 gauge) and crimped. The ferrule needle can then be cut to size to fit into an interface card or terminal block. As ferrules come in a variety of colour-coded sizes they can be used for a variety of wire gauges.
A special crimper tool is used to 'crimp' the ferrule in place securing the wire.
LEFT: 1mm red ferrules connected to a terminal block. They look neat, protect the wires and allow for easy removal without damage to thin wires (click to enlarge).
I’ll submit that ferrules are not suitable to use everywhere; however, for certain applications they are useful to have in your simulator-building toolkit.