As shown in the illustration of the fuel injection pump, the section designated as "M" is referred to as the __________. Illustration MO-0061

Correct Answer: Option A — plunger helix

The plunger helix is a machined, slanted groove on the pump plunger that regulates effective stroke length. As the governor rotates the plunger, the helix uncovers the spill port earlier or later, precisely controlling the quantity of fuel injected per cycle.