🔍 Key Concepts

• Class of fit refers to how tight or loose the mating threads are, not how many threads per inch (TPI) there are. • Thread pitch/threads per inch (TPI) is a separate concept from class of fit; different fits can share the same TPI. • Higher class numbers generally mean a tighter, more precise fit; lower class numbers mean a looser, easier-assembling fit.

💭 Think About

• Ask yourself: does changing from class 1 to class 4 automatically change the number of threads per inch, or just how snugly the existing threads mate? • Think about which class is commonly used for general-purpose bolts and nuts, and which are used for very precise, high-accuracy fits. • Compare in your mind: if you want a part that assembles easily even with some dirt or damage, would you pick a lower or higher class number?

✅ Before You Answer

• Verify that class of fit ≠ threads per inch (TPI); they are defined separately in thread standards. • Check whether higher class number means tighter or looser fit in standard machine practice. • Confirm which statement compares relative tightness/looseness correctly between the mentioned classes (1, 2, and 4).