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 (11, 12) 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 (21, 22) 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 (11, 12) of the first electrically conductive portion and the extensions (21, 22) 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 (11, 12) 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 (21, 22) 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 (11, 12) of the first electrically conductive portion and the extensions (21, 22) 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.