This black PVC airline,tube is made from quality food grade virgin PVC used in the food industry, so rest assured its safe to use in your Koi pond,Fish tanks etc.
It has excellent flexibility and ageing resistance with high resistance to acid and alkalis for use on air products and water.
4mm internal diameter 6mm external diameter(approximate).
4mm internal diameter air line is the standard size that fits most small air pumps,air pump manifolds,and air stone.
If unsure please ask.
Smooth bore non toxic ideal for cold water, Tropical, Marine and Pond water.