A comparator tool is provided for evaluating the profile of a multi-lobe helical rotor. The comparator tool includes a housing with a first end and a second end and an internal bore extending from the first end to the second end. The internal bore includes a first diameter having nominal clearance for an original equipment manufacturer (OEM)-specified major diameter of the rotor, a second diameter having nominal clearance for an OEM-specified minor diameter of the rotor, and multiple helical grooves corresponding to a number of lobes in the helical rotor. Each of the multiple helical grooves has nominal clearance for an OEM-specified tip diameter of the rotor. The comparator tool slides along the length of the rotor and provides visibility of an interface between a circumference of the rotor and the first end at any place along a length of the rotor.