In order to allow the user to see which cam surface (one of surfaces 60 e 1-60 e 8) is arranged in the path of the stop projection 30 j (i.e., to adjust the desired depth setting) the upper body part 100 has a window W (e.g., a through opening) through which one can read the indicia (e.g., numbers or other desired indicia such as letters or marks) of the cam disk 60.