Hydraulic Mandrel, Gear Grinding mandrel, Gear Clamping Solution, Clamping System, Mnadrel, Expanding mandrel. Rotary CONCENTRIC. mandrel manufacturer, Hydraulic Mandrel manufacturer. A hydraulic arbor is a fully closed system with no external hydraulic power supply and no moving parts. It is the most compact work holding method, and it is capable of clamping multiple parts. The outside dimension of a hydraulic arbor expands to clamp the inside dimension of a gear when hydraulic Jelly (REX SUH 25) is forced into the bladder of the arbor. They are available in sizes from 6 mm to 1, 000 mm. Hydraulic arbors are an option to maintain the highest radial and axial run-out, provide concentric clamping and ensures roundness. Additionally, vibration is nearly eliminated due to the large uniform clamping surface.