BaByliss FX775U Replacement Comb 13mm fits Forfex Trimmer FX770U Precision Definer. Available in different sizes, the BaByliss Replacement Combs allow the user to cut hair to a specific length or helps them to create a different style. To Remove: Pull the sides of the comb attachment away from you and remove the comb. To Replace: Turn the clipper to the off position, slide the comb attachment into the blade, push down on the tab at the back of the comb attachment until you hear a click, ensuring the sides of the comb are securely in place.