7005.21 - Colored throughout the mass (body tinted), opacified, flashed or merely surface ground:

This HTS classification pertains to flat glass sheets that are "colored throughout the mass (body tinted), opacified, flashed or merely surface ground." This means the glass is manufactured with color integrated into its structure, or it has been treated to be opaque, features a flashed layer, or has undergone a basic surface grinding process. The key characteristic is that the glass retains its essential form as a sheet and has not been subjected to more advanced working operations beyond these specific treatments.

The distinction from sibling category 7005.29, which covers "Other" nonwired glass, lies in the specific treatments applied. While 7005.29 encompasses other types of nonwired glass not otherwise specified, this category is reserved for glass that exhibits body tinting, opacification, flashing, or simple surface grinding. This focus on the method of coloration or surface alteration is crucial for accurate classification.

Within this category, further subdivisions are based on the physical dimension of the glass: thickness. Subcategory 7005.21.10 covers glass measuring less than 10 millimeters in thickness, while 7005.21.20.00 addresses glass measuring 10 millimeters or more in thickness. This differentiation by thickness is a common criterion in glass classification, reflecting different manufacturing processes and end-use applications.