Abstract: A rugged lightweight valveless plunger (38) is provided for use in a well pumping system of the free plunger type. The plunger (38) comprises an elongated cylindrical integral aluminum body (42) having a rigid sealing section (44) formed by a plurality of circumferential grooves (46) defining a plurality of annular sealing flanges (48). The flanges (48) and grooves (46) are uniform and closely spaced. A pair of annular steel collars (50, 52) are secured to the aluminum body (42) on opposite longitudinal sides of the sealing section (44) and have an outer diameter substantially equal to the outer diameter of the annular sealing flanges (48). The aluminum body provides lightweight and ease of machinability. The collars (50, 52) protect the annular aluminum sealing flanges (48) from frictional wear against the well tubing (20), such that sealing tolerances are maintained over an extended life rating. The plunger (38) is simple in construction and virtually indestructable.