The Refill Friction Stir Spot Welding (RFSSW) method consists of three variable process parameters: rotational speed, tool plunge time and depth. The article presents an analysis of the effects tool plunge depth on shear strength. For this purpose, samples had a shearing load applied in a device prepare for this purpose. The shear strength was determined. An analysis of the results showed that tool plunge has a large effect on the strength of the joint and the structure of the joint. Depending on the tool plunge value, three types of joint failure were observed during the static shear strength test.