Through-hole technology (tht) is a mounting system. Whereas surface mount technology (SMT) has very small or no leads and are directly mounted on the printed circuit board (PCB), through-hole (also spelled thru-hole) technology uses leads on the components that are inserted into holes drilled into a printed circuit board, and those leads are then soldered to pads on the opposite side. They come in either a radial lead, which protrudes in parallel from the same surface on a PCB, or an axial lead, which runs along the axis of symmetry of the component.

Through-hole mountings have very strong physical bonds to the PCB board since they are soldered from both the top and bottom of the board. This makes them very durable with a high environmental and power tolerance. Because of this, as well as their high heat tolerance, through-hole mounting (THM) is more robust and is still used in outdoor applications, and even used in aerospace and military applications.