Hard covers are protective covers that are used to protect books, magazines, and other printed materials. The term 'hard covers' can be broken down into two crossword solutions: crusts (6 letters) and scabs (5 letters). Crusts are a hard outer layer that forms on the surface of something, such as bread or a wound. Scabs are a dry, hard crust that forms over a wound or sore as it heals. Both crusts and scabs are hard and protective, making them an apt description for hard covers.