Positive-engaging coupling for a portable handheld tool

A positive-engaging coupling between a drive part and a driven part, the positive-engaging coupling comprising:

• one of said parts having an insert portion defining a first noncircular cross section;
• the other one of said parts defining a receptacle for accommodating said insert portion therein and said receptacle having a second noncircular cross section corresponding to said first noncircular cross section and being selected to ensure a positive-engaging coupling between said parts which permits one of said parts to drive the other one of said parts;
• said first noncircular cross section having dimensions less than said second noncircular cross section so as to cause said insert portion and said receptacle to conjointly define an intermediate space when said insert portion is inserted into said receptacle with said space being sufficiently narrow to retain and said positive-engaging coupling between said parts;
• an elastic insert inserted into said receptacle for filling out said intermediate space when said insert portion is disposed in said receptacle;
• said intermediate space having a width B;
• said insert being an annular member having a uniform wall thickness D corresponding approximately to said width B of said intermediate space;
• said insert having a cross section corresponding to at least one of said first noncircular cross section and said second noncircular cross section;
• said insert having an annular flange formed thereon;
• said one part being a shaft having said insert portion formed on one end thereof;
• said shaft having a shoulder formed thereon between said insert portion and the remainder of said shaft;
• and,
• said receptacle having an end face adjacent said shoulder and said annular flange being clamped between said shoulder and said end face.