In rehabilitation engineering and assistive technology, precedent researches have focused on a single characteristic or property of a single joint, while little attention was paid to similarities among joints. This work attempts to investigate similarities among human joints by referring to the coding system of human joint properties proposed in Part 1. To investigate the similarities, eight out of the nine properties in this coding system (except the locations of joints) are divided into five cases. In Case 1, we consider the numbers of bones involved in joints and shapes of joint surfaces. In Case 2, we consider the directions of rotation, directions of translation, and numbers of axes of joints. In Cases 3, 4 and 5, the functions of joints, arthrokinematics of joints, and weight bearing of joints are considered respectively. Similarities among the 41 kinds of joints in this coding system are hereby investigated by sorting the joints' codes in each case. As results, the 41 kinds of joints are classified into 12, 13, 3, 6 and 2 groups in Case 1 to Case 5 in sequence. Regarding the properties discussed in each case, joints in the same group possess similar properties. However, four groups in Case 1, four groups in Case 2, and one group in Case 4 each have only one kind of joint, which is unique, having no similarities with other joints in the properties considered. In conclusion, similarities among human joints are discovered systematically by referring to the coding system proposed in Part 1. These similarities offer an innovative and utile reference for assistive technology device designs and other pertinent research. Similarities beyond these five cases can be further investigated with the same method.