A shim coil device for installation andor arrangement within a local coil of a magnetic resonance device is provided. The hollow fibers according to the invention are obtainable by processing a spinning mass to a hollow fiber according to general methods, by curing said fiber thermally, via radiation induction or via chemical induction, and by removing the organic components via pyrolysis. A first hard region is at the axial forward end of the tooth body and defines at least one distinct cutting edge that has an orientation to engage the stump during operation.