I have a friend who had a (very) old circular trim saw that is clearly labeled “SKILSAW Model 504 4-1/4″ Light Duty”.  Her most pressing need is a source for sawblades (with a 1/2″-diameter bore), but she would also like to know a bit about the history of this saw model, as it belonged to her father.  I’ve tried search engines with all the phrase combinations I could think of and have struck out.