As per tractor starter motor wiring diagrams, current is passed through the stator and the armature at the same time. The Tractor Starter produces a fixed magnetic field that can be likened to the force of a strong permanent magnet.

All tractor starters used on tractor engines are similar in design. The only varying factors for tractors starters is the operating voltage, amperage range, KW rating, the number of engaging teeth on the front gear, and the direction of rotation of the central starter shaft, whether its counter clockwise (CCW) or clockwise (CW). These are basic factors that all starters will have in principle and design.

A starter for tractor motor is built around Flemings left had rule, which states that a conductor (copper wires, called armature) carrying a current (dc power), when placed in a magnetic field (produced by a stator) will experience motion perpendicular to the flow of the current (the movement of the starter motor shaft)

The heart of the tractor starter is the central laminated iron core, onto which are wound conducting copper wires that form a conducting ring at one end of the shaft. This ring is called a commutator.

The central laminated core is made of up several thin layers of sheet metal, with the copper wires wound around and in between the iron sheet layers in a predetermined manner. This entire component, with the shaft, sheet metal and copper wires are then laminated and cured in a furnace. The laminations ensure that there are not electrical shortages between the three components.
The laminations and the copper wire are separated by thin pieces of paper, which are then kept intact by the lamination process, and appropriate string.

When a current is applied to this copper winding, a magnetic field develops. The Loops of wire used is called an armature.
This entire laminated armature shaft is then placed in to the starter motor housing. Onto the housing of the starter motor is fixed more sets of copper wire loops, called a stator. The armature spins inside of the stator via bushings and bearings. The clearance between the two can be as little as a millimeter.