that I'm not sure ... maybe 1890's to about 1940 . it could be a Yale , U.S. or other type Nalc . I'm really not up on my padlock types. there is some reference links in the ye olde relic hunter's resource guide stickied at the top of the main page in the relic section. here is the link to that page http://www.americandetectorist.com/forum/showthread.php?759-Ye-olde-Relic-Hunters-Resource-Guide