Mesh

Meshes are objects in Roblox that greatly modify the appearance of an object.

There are SpecialMeshes, which contain the most variations, and BlockMeshes and CylinderMeshes, which were made for the Head system.

Every Hat and Gear, with the exception of the first four stages of the Mysterious Box (Which later became the rubber duck hat), has a SpecialMesh inside it.