Mishná sobre Daniel 3:35

A metal spindle-knob:Rabbi Akiva says it is susceptible to impurity But the sages say it is not susceptible. If it was only plated [with metal] it is clean. A spindle, a distaff, a rod, a double flute and a pipe are susceptible to impurity if they are of metal, but if they are only plated [with metal] they are clean. If a double flute has a receptacle for the wings it is susceptible to impurity in either case.