🔍 Key Concepts

• Common nominal pipe sizes used in marine piping systems • Difference between standard fractional pipe sizes and less common intermediate sizes • How pipe sizes relate to standard fittings and threads (like NPT)

💭 Think About

• Look at the sequence of sizes and think about which ones you see most often on drawings, valves, and fittings aboard vessels. • Consider hardware stores or shipyard stock: which sizes of threaded pipe and fittings are typically on the shelf, and which would be harder to find? • Ask yourself which size would complicate ordering standard valves, unions, and couplings because it does not match usual nominal pipe size series.

✅ Before You Answer

• Compare each option against the most typical small-bore sizes: 1/4, 3/8, 1/2, 3/4, 1 inch • Think about which size you have actually seen stamped or marked on valves, elbows, and tees in practical use. • Eliminate the sizes that clearly match the common nominal series, then focus on the one that does not fit the usual step pattern.