Glue gun is used to melt keratin adhesive glue sticks. For professional useage only. Glue gun has 10-12 wattage of heat and can be used to pretip hair extension.
 
How to apply glue to hair extension with glue gun:
Insert keratin glue stick into glue gun. Wait until you see melted glue from tip of glue gun. Press handle and place small bead of keratin glue on a few strands of hair. Make sure you place the glue at the tip of hair extension before applying to hair.