TemplarSmith

Im sure this has been answered so im sorry. I tried searching the forums and the internet for it but i couldnt find anything helpful. I just need to know what type of spring you would use for a treadle hammer? And maybe a rough ballpark of how strong it should be? (i know nothing about springs) Its for a very basic treadle. Probably like a 10lb sledge. Thank you for your time!!!