Abstract: A bypass plunger formed as an integral one-piece hollow body-and-valve cage unit retains a dart valve within a valve cage section of the hollow body with a threaded retaining nut that may be secured by crimple means. A boundary zone, defined along the plunger body, where the integral valve cage section adjoins the plunger body, is configured with a uniform outer diameter to maximize the plunger body wall thickness and durability of the one-piece bypass plunger. The valve cage may have flow ports configured with ramps at an angle with the longitudinal axis to control flow through the flow ports during descent of the bypass plunger. A clutch assembly using garter springs with split bobbins may be disposed within the valve cage portion of the one-piece bypass plunger.