Stylets are malleable metal rods which are covered with a clear plastic sheath with a more or less atraumatic tip.
Note that the Broncho-Cath Endobronchial tube is supplied with its own stylet.
Stylet as supplied right out of its sterile packet
Stylets are used inside an endotracheal tube to give it a certain shape which aids navigation of the tube towards the laryngeal inlet.
Many practitioners feel that the routine use of a stylet with a standard endotracheal tube and conventional laryngoscopy is unneccessary and increases the risk of accidental trauma to the airway without clear benefits in a majority of patients. The standard endotracheal tube's 'natural' curvature is usually bent enough for most cases of laryngoscopy to place the tube through the vocal chords without loading it onto a stylet.
In contrast, the armored/ reinforced tube usually requires a stylet as it is more 'floppy' than the standard endotracheal tube and does not maintain a 'natural' curvature well during intubation.
Although stylets are malleable they should be considered rigid intubating aids and therefore never be advanced into the patient's larynx or trachea due to the risk of causing significant trauma.
Using the stylet correctly, i.e. with its tip located well within the lumen of the ET tube (see pictures above), you should stop advancing the ET tube into the trachea once the tip of the ET tube (but not the tip of the stylet) has just passed the vocal chords. Then withdraw the stylet, or ask an assistant to do so, while holding the tube steady before advancing it further into the trachea.