Which type of bit has ridges referred to as flutes?

Carbide bits are specifically designed with ridges known as flutes, which play a critical role in their function. These flutes help the bit efficiently cut through the nail material, providing a smoother and more controlled removal process. The design allows the bit to create less heat during use, which can be beneficial in preventing damage to the natural nail or surrounding skin.

Sanding bits, on the other hand, typically feature a smooth surface that is intended for buffing and finishing, rather than cutting. Ceramic bits, while durable and effective for certain applications, do not have flutes; instead, their structure allows for precise filing with minimal dust production. Diamond bits are characterized by their grit-encrusted surface, designed for strength and longevity, but they lack the flute design seen in carbide bits. Thus, the distinctive fluted design of carbide bits is what sets them apart, making them the correct answer for this question.