I decided to resurrect a thread Duane started in “Parts Wanted” that began as a simple key blank request, and as often happens on V8, it expanded into a broader key discussion. I’m continuing it here because, to me, “Paper Trail” is where documenting-info-related topics should be. Back when I learned there were no official documentation sources for ‘71s, I became determined to learn all I could about mine. Luckily I had the Owner’s Manual and POP, a great starting point, but none of the “holy grail” stuff like window sticker, IBM card, POBF, or invoice, which brings me to key codes. Based on my glovebox key wear, I was confident it was original and I would find code on lock (for ’71, codes only on glovebox and ignition housings). Success. My ignition key is a Curtis replacement with slight wear. Patina on ignition lock told me there’s a good chance it’s original too. I had 2 options; pull tilt column lock, or “reverse engineer” key. Reverse engineering appealed to me on 2 levels; I didn’t have to take my tilt column apart, and I’d learn more about keys from reverse engineering; I recently researched my dealer’s ’72 Sloan data for option ordering patterns, reverse engineering data to help determine originality of some options on my ‘71. If your locks were replaced and you don’t have IBM card, “build sheet”, knockouts, original keys, codes recorded by original owner, or an official source like Sloan, you’re done, but by just having original keys, you can reverse engineer their codes. Doing this only makes sense for those with keys and no locks (or documentation geeks). If you have original locks, get codes there. There were only 8 different (4 pairs) GM key blanks from ’68-’82. The first blank in pair was square-head “primary” (usually ignition) key, second was round-head “secondary” (usually everything else) key. Primary/secondary blank in pair was stamped with letter A/B, C/D, E/H, or J/K. All 8 key profiles are different and only fit respective locks. Pairs were reused in a four year cycle, starting in ’68 with C/D, ’69 was E/H, ’70 J/K, ’71 A/B…and so on. Each key in pair is identified by a 4-character key code from the following subsets; C/D - “C” 0N00 thru 9N99 and 0P00 thru 9P99, “D” 0R00 thru 9R99 and 0T00 thru 9T99 E/H - “E” 0J00 thru 9J99 and 0K00 thru 9K99, “H” 0L00 thru 9L99 and 0M00 thru 9M99 J/K - “J” 0E00 thru 9E99 and 0F00 thru 9F99, “K” 0G00 thru 9G99 and 0H00 thru 9H99 A/B - “A” 0A00 thru 9A99 and 0B00 thru 9B99, “B” 0C00 to 9C99 and 0D00 thru 9D99 Now you know enough to help verify “build sheet” documentation; I’ve seen a ’71 POBF with all-numeric key codes, hmmm… Each key code is associated with a 6-digit “number” with each digit being 1 to 5, representing depths for each of the 6 cuts, starting at base, to make blank into a key. To decode, measure .109” from shoulder, mark key, then measure .092" from each mark for rest. Measure root depth at each mark for cut value. I used a dial caliper micrometer. For final step, you need access to a GM Key Code Book that covers your year. I bought one on eBay and found my primary code, with about as much trouble as doing Sloan research. Now for keys, there are several brands, Curtis, Ilco, and Strattec come to mind. Strattec is licensed by GM and has correct OEM “Mark of Excellence” logo on each side. Logos are not as crisp as originals and they don’t have knockouts, so if that’s an issue, you need to find originals. I’m told they are nickel-plated brass like originals for now, brass is expensive. I want to weather a replacement primary key to match my original secondary, so Strattec should work for me. 10/18/2020 Addendum: Some additional info found after original post. Strattec uses a generic keyway that works for all years rather than year-specific profiles. Original key letter code orientation depends on manufacturer. Briggs & Stratton had letter oriented to be read with key vertical, Rochester Products (per Chief, B & S Automotive Locks Division) were oriented with key horizontal.