These terminal blocks are designed to 'snap' together. You can attach as many 3-pin or 2-pin ones along as you'd like to make arbitrary length of terminal block. These particular 3.5mm terminal blocks are our favorite: big enough for a range of wire gauges, easy to adjust with a screwdriver, and not too chunky. The only down-side is that they do not fit into 2.5mm spaced holes - but they do fit in most perf/proto-board if you rotate them diagonally . They don't fit nicely into solderless breadboards. Nothing makes a project harder to maintain than a lot of loose wiring. That's why we like to use terminal blocks whenever making PCB-to-Wire connections. It is installed on the PCB board. Used widely in the electronics, communication equipments, instruments, calculator, automatic control system, domestic appliance and warning devices, etc.