This is a TUBULAR or BARRELL type replacement key for ACE Locks and a replacement tubular key for CHICAGO LOCKS. Key will be precut and ready to work in the lock. A key blank is pictured to help with identification. On the lock where the keys enters or on the side of the lock, you should find a letter prefix (AB001), a letter suffix (210AB), both a prefix and suffix (C210AB), letter between numbers (2RR50), or just number with no letters (123). If it's worn down and hard to see, sometimes a magnifying glass will help. and flashlight. You could also place a piece of paper over the key number and then shade over it with a soft pencil. SAVE 15% Buy $15 or more and then use the code LOSTAKEY in the discount code redemption box during checkout!