This silicone airline has excellent flexibility and ageing resistance with high resistance to acid and alkalis and ozone resistant 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.
Completely fish safe material used.
Smooth bore none toxic ideal for cold water, Tropical, Marine,koi and pond water.