A cover for magnetizing a shaft of a tissue-penetrating medical device is disclosed including a sleeve member having a hollow body to form a protective closure over the shaft of the tissue-penetrating medical device. The proximal end of the hollow body provides a receiving space for receiving the shaft of the tissue-penetrating medical device. One or more magnet is disposed on the sleeve member. A magnetic shield composed of one or more shielding materials associated with the cover that minimizes any effects to the clinical environment from magnetic fields generated within the cover. Medical devices and methods of magnetizing the shaft of a tissue-penetrating medical device using the cover are also disclosed.