🔍 Key Concepts

• Prussian blue as a marking compound in mechanical fitting • How technicians verify contact between two machined metal surfaces • Difference between leak detection methods and contact/fit-checking methods

💭 Think About

• Which choice involves needing to see where two metal parts actually touch each other? • For each option, ask: would I need a visible colored transfer stain, or would I need pressure/soap/electronic detection instead? • Think about common shop practices in machine work: where have you seen blue dye or paste used?

✅ Before You Answer

• Match Prussian blue with its role as a color-transfer marking compound, not a fluid that reacts to refrigerant or heat. • Eliminate any answers that involve leaks in piping or systems, and focus on solid-to-solid contact. • Ask: which option specifically requires checking the evenness and area of contact between parts?