Lot of 5 Master padlock M1 Key Blanks stamped "Do Not Duplicate".  This key blank is used on the most common Master padlocks, including the #1 lock, as well as many of the midsize padlocks made by other companies.  You can get cut the blanks cut locally for greater key control.  Locksmiths and most reputable hardware stores will refuse to make copies of stamped keys.  It will not prevent all duplication, including the self serve key kiosks, but many people will be hesitant to try getting them cut.  If you are unsure if these are the correct keys for you, please email me a picture of your key before ordering.