Replacing TENS electrode pads can be confusing, especially if purchasing for a secondhand Tens machine. Electrode pads come in a variety of sizes, shapes, connections and quality. The size and shape of the Tens pad will be determined by personal preference and their suitability to the part of the body for which they will be used. For example, large rectangular Tens pads are ideally suited to treat large areas of the body such as the back, abdomen and thigh; the smaller round pads are more suited to treat areas of the face or more tricky areas such as the knee or elbow. The square electrode pad is the most common shape of Tens electrode pad and probably the most versatile, it can be used appropriately on almost any area of the body and is more suitable for targetting specific pain