When I rebuilt the transmission for my D250 Cummins, the trans cooling lines were rusted to the point of breakage. And they are 1/2 od !!!. Not available from the dealer anymore. So I bought a coil of 1/2 copper and flared and bent them into position myself. No leaks yet in a year and a half. In my case, they travel pretty far from the radiator before they are clamped tight to the trans.