A set includes 40 circular protective covers + 40 square protective covers. The classification method is up to you:
By "Area": Circular red covers for door keys, square blue covers for bedroom keys, circular green covers for balcony storage cabinets. Just by looking at the shape and color, you can tell which one to open without even looking at the keys themselves;
By "Purpose": Yellow for commonly used keys (such as the front door), purple for backup keys (such as the storage room), when needed, just glance at the color, and the usual key will immediately stand out;
No worries for many people: Each roommate in a shared apartment gets a different color. Parents use dark colors, and even if the key chain is messy, you can still quickly identify "which one is mine".

Includes a household key, just the right size
Not all keys can fit? This one is specially designed for common household keys:
Round style: Diameter 0.87 inches, suitable for small drawer locks, mailbox keys (key head 0.7-0.9 inches);
Square style: Side length 1.1 inches, suitable for most security doors, interior doors keys (key head 0.8-1 inch);
These keys cannot be used: Be careful, the ignition keys for cars, motorcycles, and boats are usually thick and have buttons, they won't fit.