(1) The caps should be of the internal plug type: Once fastened, the caps should not fall off easily; they should be easily removable without the need for additional tools.
(2) The material of the caps should be high-pressure grade one recycled material (polyethylene or polypropylene).
(3) The caps should have a uniform color without any color difference. The outer surface should be smooth and delicate in both appearance and touch. The outer edge should be neat and free of burrs. The text on the caps should be clear, prominent, and visible.
