Wire ferrules (also called bootlace terminals) are crimped onto stranded wires that are being inserted into terminal blocks. They protect the wire and keep the strands together to avoid strays shorting to adjacent terminals.
How to Choose Hex or Square crimp profile? Both of Hexagonal or Square Crimp provides stable connection on end sleeve ferrules. Square crimps fit better into rectangular shapes and that hexagonal crimps fit better into round shapes. It depends on what style of terminal block you are using.