This is a compact and roller type one-way clutch which formed a cam face on its outer ring (available shaft diameter range: 6 to 35 mm).  When the outer ring begins to turn in the counterclockwise direction (direction marked on the outer ring width surface) relative to the shaft, the force of spring causes the rollers to advance to the engagement positions on the outer ring cam face, thereby the wedge action taking place between the outer ring cam face and the shaft drives the shaft. When the outer ring rotates clockwise against the shaft, the shaft rotates counterclockwise relatively to the outer ring and, as a result, the rollers get away from the outer ring cam face and simultaneously the outer ring idles against the shaft. As both sides of the outer ring are oil-impregnated, no additional bearings are needed.

The NCU series comprises units made up of an outer ring, lid, roller, cage and spring. The outside has resin external parts including a gear, pulley and roller receptacle to make up the unit. The external execution is the same as the NHF series. The gears, pulleys, rubber roller receptacles and other external parts are made of polyacetal resin. Similar components in polyamide resin are also available.