I choose an AC motor (IEC) with frame number 71. The key on the shaft of the motor is $5mm,$, $4.23 mm$ and $6 mm$ in diameter. At other hand i cant't find a safety coupling (torque limiter) with exactly the same dimensions as the key way on the motor. They are all a bit smaller or bigger but they have the same diameter as the motor. for instance $4 mm$, $2.23 mm$ and $6 mm$ in diameter.
what can i do ? Is it possible to use a slightly greater safety coupling or the dimensions of the both, should exactly be the same ?