For maximum performance change heads once a year. Replacement heads fit Spectra 8 Spectra 7800XLCC 7100 and 7200 Series only. Does not fit any other Philips Norelco Razor Models. Contains 3 cutters and 3 combs. Directions: How To Change Your Philips Norelco Razor Heads: 1. Remove plug from outlet and cord from razor. 2. Press razor head release button. Open the razor head assembly and remove assembly from razor body 3. Turn the wheel counter clockwise and remove the retaining frame. 4. Remove used cutters and combs and insert new ones. Remember: Each new cutter and comb is a matched set and should not be inter changed. Place the new ones in the razor assembly in such a way that the sides with the little holes and slots point to the middle of the shaving unit. Make sure that the 2 pointy edges of the razor heads fit exactly into the recesses. 5. Replace frame on the razor unit by pressing down the wheel of the retaining frame and turning it clockwise. 6. Replace razor head assembly back on razor. Place the protective razor head cap on razor to protect heads. Important: If you accidentally interchange the cutters and combs it could take several weeks before optimal shaving performance is restored. Replace damaged or worn razor heads with Norelco HQ8 Spectra razor heads only.