A paddle wheel flow meter designed for measuring the flow rate of a viscous or debris-laden fluid with fewer parts, higher durability and simplicity of servicing. The flow meter includes a housing including a flow bore and an insert body with an integral rotor shaft. The insert body is removably insertable into the housing. A rotor includes rotor blades and is attached to the rotor shaft so as to be at least partially located in the flow bore such that flow of the fluid causes the rotor to rotate. A sensor unit generates a signal indicative of the rotational rate of the rotor, which can be used to determine the flow rate of the fluid.