How much slack should a faucet supply line have?

Flexible braided connectors seem easier to align under a bathroom sink, while rigid or semi-rigid tubing can keep the space tidier. But neither is a good choice if the ends don’t match the faucet and shutoff, or if the line has to be forced into place.

How do you verify the connection sizes and thread types before choosing a line? For length, is the goal simply a gentle curve with enough slack for access, but no loops or tension? I’d also like to know what visible signs suggest a connector is kinked or stressed rather than just routed awkwardly.