Looks mid 50s. I think it should have the s/n stamped on the BB. Prefix should be 'MOD 502', and the second will either be a 4 digit number, likely in the 4500 series, or a 3 digit in the 200 series. The 4 digit is a catalog #, and if you post that, I'll see if I can find it in my Elgin/JC Higgins?Hawthorne book. If it's the 3 digit, that's the actual model number, and you might be able to get some info at sears parts direct online, but usually not. -Adam