Mermaid Tail to the Beach - Stone Car Coaster. Round Car Coaster. This absorbent stone coaster has a mermaid just giving you a friendly reminder to get your tail to the beach! It measures about 2.625" in diameter x .3125" thick and fits most car cup holders. Having a small coaster like this is a great way to protect your car by catching the drips before they run off of your drink and onto your car upholstery!