In electromagnetism, to determine the direction of the electromagnetic force and magnetic field, the right-hand rule (RHR) is used. Previous researches show that students have difficulty in applying the RHR. This research is aimed to find out the factors which make it difficult for the students to apply the RHR. To achieve this, qualitative case study design is used and 270 students who took Basic Physics II course at university participated. The Right-Hand Rule-Diagnostic Test (RHR-DT) and the unstructured interview were used as data collection tools. In the analysis of the data, firstly, the right-hand types used by the students were determined. Then the right-hand types used by the students in the solution of each task are presented. After that, eight of these students were interviewed about their RHR-DT answers and those interviews were video recorded. Video recordings are divided into three categories according to the level of students: upper, middle and lower. According to the results of this research, it can be said that the conceptual understanding of electromagnetism, the vector algebra and spatial cognition effect the usage of the RHR. In the light of research results, suggestions were made for the teaching of RHR to physics teachers.