Each shaving head consists of a cutter and a guard, with a retaining ring to hold them into the shaver unit (otherwise known as the shaving head holder). Each cutter and guard forms a unique set, so always try and return each cutter to its respective guard after cleaning. Place the cutter into the guard with the blades facing downwards.
When you use the retaining frame to lock the shaving heads back into the shaving unit, ensure that it is locked firmly into place. When the retaining frame is attached correctly, it should not lift off if you attempt to separate it from the shaving unit.
If your shaver model has shaving heads that slot into the retaining frame before being locked into the shaving unit, ensure that the notches on the shaving heads are in the projections of the retaining frame (see illustration below).
For detailed instructions on removing and reattaching the shaving heads, please refer to the user manual provided with your product.