"Pets Collar 3" most commonly refers to an Elizabethan collar, or "E-collar," that is a size 3.

Elizabethan Collars (E-Collars): These are the cone-shaped collars used to prevent a pet from licking, biting, or scratching a wound, stitches, or an irritated area while it heals. The sizing is not standardized across all manufacturers, but a size 3 is generally for a small to medium-sized animal. For example, some brands might size a number 3 collar for a cat, while others might size it for a small-to-medium dog. The collar's size is determined by the neck circumference and the length from the neck to the end of the nose.

Other Collar Types: The number "3" could also refer to:

The length of a standard collar in inches (e.g., a 3-inch collar for a very small pet).

The width of the collar in centimeters (e.g., a 3 cm wide collar).

A product's name or model number, such as "Pet Collar, 3 Asst." or a "Size 3" within a specific brand's sizing system.