FAA Aviation Mechanic General (AMG)Materials, Hardware and ProcessesEasy
A technician is reviewing a material specification sheet for a landing gear bolt marked SAE 4130. What does the "41" designate in this steel numbering system?
- AA nickel-chromium stainless steel series
- BA tool steel series hardened by air cooling
- CA plain carbon steel with no alloying elements
- DA chromium-molybdenum alloy steel series
Show answer & explanationAnswer & explanation
Correct answer: D. A chromium-molybdenum alloy steel series
In the SAE/AISI four-digit steel numbering system, the first two digits identify the alloy type; "41" designates chromium-molybdenum alloy steel, while the last two digits ("30") indicate approximately 0.30% carbon content.
Why the other options are wrong
- A. Stainless/nickel-chromium steels use different series designations (3xx).
- B. Tool steels have separate letter-based designations, not this numbering system.
- C. Plain carbon steels are designated 10xx, not 41xx.
SAE Steel Numbering System
A four-digit code identifying alloy composition; the first two digits indicate alloy type and the last two indicate approximate carbon content in hundredths of a percent.
- 10xx = plain carbon steel
- 41xx = chromium-molybdenum alloy steel
- Last two digits = approximate carbon percentage x100
- 4130 and 4340 are common aircraft structural steels
Memory trick: "Forty-one, forged with chrome and moly, tough as can be."