A tubular spring is provided for receiving and pretensioning a piezoelectric or magnetostrictive actuator of an actuator unit, e.g., for actuating a fuel injector valve in internal combustion engines, wherein the tubular spring comprises at least two types of recesses, each comprising different maximum lateral extensions in the longitudinal direction of the tubular spring. The tubular spring is designed to comprise a uniform load distribution about the circumference of the tubular spring even without welding the longitudinal sides thereof abutting one another.