Making metal clay tubes for hinges or other components can be tricky, especially if you don’t have a metal clay extruder with a special die to make tubing.
I’ve got a low-tech solution that uses an inexpensive set of tools called a “transfer punch set” (available from Harbor Freight Tools, www.harborfreight.com). The transfer punch set consists of 28 5-in. (12.7 cm) round steel rods ranging in diameter from 3/32 in. (2.4 mm) to a little over 1/2 in. (13 mm), in increments of 1/64 in. (0.5 mm).
By pairing one of these punches with round brass tubing that has a larger inside diameter than your punch, you can make metal clay tubes in a jiffy.
Lightly oil the inside of your round brass tubing, and push wet metal clay into it. Using your punch like a plunger, insert the punch's pointed end into the wet clay to form a metal clay tube inside the brass tubing.
Allow the clay to dry completely. Then, carefully twist and pull the metal clay tube out of the brass tubing.