What type of beetle is characterized by being round and measuring between 1/2" to 3" long?

The metallic wood beetle is distinguished by its rounded shape and size, which typically ranges between 1/2" to 3" in length. This beetle is often noted for its vibrant metallic coloration, which can vary among species. The rounded body shape, along with its size, helps to specifically identify it among various types of beetles.

In contrast, other beetles listed typically do not match this distinct physical description. Bark beetles tend to have a more elongated body and are smaller in size. Long horned beetles are characterized by their long antennae and body shape that is more elongated rather than round. Flathead beetles, while sometimes having a rounded appearance, are also distinct in body structure, as they typically have a flattened head and a broader shape at the front. Thus, the defining features of the metallic wood beetle align perfectly with the description presented in the question, making it the correct choice.