Safety Door Knob Covers help keep your children safe by preventing them from opening doors or getting locked in a room. Compatible with standard spherical doorknobs. Bigger size covers fit more door knobs than any competing product. Polypropylene fiber material, which is odorless, non-toxic, non-polluting and stronger to prevent children from getting hurt. Tool-free, upgraded snaps are easier to assemble. Strong snaps and double protection lock are hard for a child to remove.