The Electrode Holder snaps onto the end of the Flexible Arm affording 3 stepped wells for holding an electrode, a reference electrode and an ATC probe. The center well has an 18mm (3/4") I.D. Side wells each have a 16.5mm (5/8") I.D. and the through holes are all 12.7mm (1/2") I.D. The Electrode Holder comes supplied with three reducing bushings for smaller diameters and five nylon cable ties for attaching wires to the Flexible Arm.