Abstract: An improved thin 3-piece oil ring 1 of an axial width not greater than 2 mm, is provided that has a corrugated spacer expander 2 of a circumferentially successive, substantially U-shaped configuration, and circular, upper and lower side rails 3, 4 holding the spacer expander 2 therebetween. The spacer expander 2 has circumferentially spaced outer crowns 5 and circumferentially spaced inner crowns 6; each of the outer crowns 5 being connected with next adjacent ones of the inner crowns 6 on opposite sides thereof by a pair of connecting members 11. The spacer expander 2 has both of the most-end portions thereof extended radially outwardly from the most-end one of the inner crowns 6 thereof forming abutting members 15, 16 for abutting each other at the point of force P.