7002.31.00.00 - Of fused quartz or other fused silica

This HTS category, 7002.31.00.00, specifically covers tubes made from fused quartz or other fused silica. These materials are known for their exceptional resistance to thermal shock, chemical inertness, and high transparency, making them suitable for specialized applications. The "unworked" designation indicates that these tubes have not undergone further processing beyond their initial manufacturing into tubular form.

The distinguishing feature of this category lies in its material composition. It is differentiated from its sibling categories by the explicit requirement that the tubes be manufactured from fused quartz or fused silica. This contrasts with sibling category 7002.32.00.00, which encompasses tubes of other glass with a very low linear coefficient of expansion, and 7002.39.00, which acts as a residual category for all other types of unworked glass tubes not otherwise specified.

As a leaf node, this category does not have further subcategories. Therefore, classification into 7002.31.00.00 is determined solely by the material of the unworked glass tube. Examples of products falling under this classification include quartz glass tubing used in the semiconductor industry for furnace liners, in scientific laboratories for distillation apparatus, and in lighting applications due to its UV transmission properties.