here are the pics I have. There isn't a cooling channel that runs the length. One of the pictures shows a second one that is made out of 1/4 round and it has a break in it that was repaired with looks like a brass solder. It is still a bit wobbly so if the fix was successful, it wasn't used in high torque situations.... I got these at an estate sale with a bunch of other steel dirt cheap. this guy had tons of large taps, dozens of files, cold chisels, antiques wrenches and planes.. I couldn't figure out the hobby that made him collect such a varied shop