(1) The pipe caps should be internal plug-type caps: they should not fall off easily once attached; and they should be able to be removed easily without the need for other tools.
(2) The material of the pipe caps should be high-pressure grade one recycled material (polyethylene, polypropylene).
(3) The color should be uniform with no color difference. The outer surface should be smooth and delicate in both appearance and touch. The outer edge should be neat with no burrs. The font on the pipe caps should be clear, prominent, and visible.
