What does it use for? What size?

1 bar =14.5 psi
10bar = 145 psi

It able to withstand max 145 psi pressure

For a sink pipe, it is more than enough

Normally used for water heater pump or house that have automated water pump

for kitchen can use stainless steel but if for water heater then should use plastic/rubber type ...

cant say cos depend on usage n many factor, just use whatever u think it is durable n suitable as long it is safe ..