Top Stop Setting Fixture-All PT (type D), STC (HVT), and Hyperbar Top Stop Injectors. Measuring fuel injector volume completed, we must test he injector plunger subassembly. (including STC (HVT) and hypervar top stop injectors). This Top Stop Setting Fixture used to the test of the injector. After the leakage testing of the injector is completed, the injector can be assembles to the point where the plunger top stop, or plunger travel setting can be made.