We should speak more specifically of a ''knob'' in all those cases in which the [[case back]] of a pen is not simply the end of the barrel, and is not used as a decorative element or as a [[blind cap]] for protection of the [[filling system]], but is instead a direct component of the latter, with the role of part of the device on which one must act to activate it. | We should speak more specifically of a ''knob'' in all those cases in which the [[case back]] of a pen is not simply the end of the barrel, and is not used as a decorative element or as a [[blind cap]] for protection of the [[filling system]], but is instead a direct component of the latter, with the role of part of the device on which one must act to activate it. |