en پژوهشي Original Research Articles <p dir="ltr" style="text-align: justify;"><strong>Objectives:</strong> Nowadays, Snap-fits are used in the automotive industry as a proper alternative for mechanical joints, cabling joints, and car interior lining joints. Due to the special form of these joints, which are assembled manually, the contact area between Snap-fits and the worker&rsquo;s fingertips can be too small. This can cause skin pain on the worker&rsquo;s&nbsp; fingertips. Therefore, an ergonomic study of these assembly operations can be useful for the automotive industries. This study was thus undertaken to investigate the severity of mechanical stress on fingertips.</p> <p dir="ltr" style="text-align: justify;"><strong>Methods:</strong> In the first stage, the FEM-Method is used to&nbsp; analyse the influence of&nbsp; some effective factors including gender, age, the thickness&nbsp; of the epidermis of a skilled worker, wearing gloves, amount of force, force angle, and snap-fit material parameters during snap-fit assembly. For this purpose, four thumb models, 50% male and 50% female from 20-29 and from 50-59 years old, are used.</p> <p dir="ltr" style="text-align: justify;"><strong>Results:</strong> The mechanical stress is directly associated with gender, age, thickness of epidermis, and the amount of force, and inversely associated with wearing gloves, and force angle.</p> <p dir="ltr" style="text-align: justify;"><strong>Discussion:</strong> The maximum compressive stress and the greater deformation of skin in the male group as compared to the female group is due to the smaller size of women&rsquo;s thumbs and a less thick outer layer of women&rsquo;s skin. Moreover, for old people, a higher elastic modulus leads to a greater stiffness of their skin. Finally, the young people&rsquo;s modulus does not have a significant effect on the maximum compressive stress and total deformation of the skin.</p> Assembly, Thumb, Snap-fit, Mechanical stress, FEM 39 48 http://irj.uswr.ac.ir/browse.php?a_code=A-10-364-1&slc_lang=en&sid=1 Hamed Salmanzadeh h.salmanzadeh@kntu.ac.ir Yes KN.Toosi University of Technology, Tehran, Iran. Mohammad Rasouli mrasouli@kntu.ac.ir No KN.Toosi University of Technology, Tehran, Iran.