An ion guiding device comprising a plurality of axially stacked plates, wherein at least some or all of said plates comprise: a first electrically conductive portion ; and a second electrically conductive portion , wherein the second electrically conductive portion is electrically isolated from the first electrically conductive portion , the first and second electrically conductive portions being shaped and arranged relative to each other so as to define an opening through which ions are axially transmitted in use; wherein, in use, a first AC or RF voltage is applied to the first electrically conductive portion and a second AC or RF voltage is applied to the second electrically conductive portion in order to confine ions radially within said opening; wherein the first electrically conductive portion has a base portion , and a plurality of extensions extending away from the base portion in the axial direction of the ion guiding device; wherein the second electrically conductive portion has a base portion , and a plurality of extensions extending away from the base portion in the axial direction of the ion guiding device; wherein the first electrically conductive portion and the second electrically conductive portion are interleaved to define a single of said at least some or all of said plates; and wherein the extensions of the first electrically conductive portion and the extensions of the second electrically conductive portion overlap in the axial direction; and wherein the base portion of the first electrically conductive portion and the base portion of the second electrically conductive portion are offset axially from each other by a gap, the gap essentially corresponding to the axial thickness of said extensions. a first electrically conductive portion ; and a second electrically conductive portion , wherein the second electrically conductive portion is electrically isolated from the first electrically conductive portion , the first and second electrically conductive portions being shaped and arranged relative to each other so as to define an opening through which ions are axially transmitted in use; wherein, in use, a first AC or RF voltage is applied to the first electrically conductive portion and a second AC or RF voltage is applied to the second electrically conductive portion in order to confine ions radially within said opening; wherein the first electrically conductive portion has a base portion , and a plurality of extensions extending away from the base portion in the axial direction of the ion guiding device; wherein the second electrically conductive portion has a base portion , and a plurality of extensions extending away from the base portion in the axial direction of the ion guiding device; wherein the first electrically conductive portion and the second electrically conductive portion are interleaved to define a single of said at least some or all of said plates; and wherein the extensions of the first electrically conductive portion and the extensions of the second electrically conductive portion overlap in the axial direction; and wherein the base portion of the first electrically conductive portion and the base portion of the second electrically conductive portion are offset axially from each other by a gap, the gap essentially corresponding to the axial thickness of said extensions. <EOS>