An external coil assembly for a transcutaneous system is disclosed. The assembly comprises: a housing having a skin-adjacent surface, an opposing exposed surface and a threaded shaft open to the exposed surface and extending toward the skin-adjacent surface; an external coil secured within the housing; and a magnet with a threaded exterior surface to threadingly engage the threaded shaft, wherein at least one of either the shaft thread or the magnet thread has at least one transverse channel forming discontinuities in the thread.