3/8 x 24 black tip

Hello there. I'm not quite sure what you're looking for. It sounds like a spiral balance. Is it for a tilt window? If so, and if you are certain the outer tube diameter is 3/8" and the balance is 24" long, the S900-24 is what you'd need. But black tips are usually not seen for the 3/8" diameter tubes. Be sure you're measuring the diameter correctly. If it's definitely 3/8", then just weigh the window sash to determine what other color tip you could use.