Depends on your need. For a key you'll only need/want to use one or two times, plastic will be able to hold up just fine. If you need something more durable, th

Depends on your need. For a key you'll only need/want to use one or two times, plastic will be able to hold up just fine. If you need something more durable, there are a number of 3d printing services that'll print whatever you want in metal without any questions asked. Desktop sintering printers are also getting cheaper and cheaper. They're still several thousand dollars, but that price will only come down now that patents are expiring and people are starting to be able to work on the processes to get them more resonable in cost.