The Vintage Singer Sewing Machine Blog: The Difference Between Domestic & Industrial Sewing Machines (or, How Not to Get Swindled on eBay & Craigslist)
Threading a vintage SINGER sewing machine 3-minute video. - YouTube
How to Thread the Singer 491D Industrial Sewing Machine : 4 Steps (with Pictures) - Instructables
Singer 281-1 Restoration: Cleaning, Adjusting, and Replacing Parts — The Mermaid's Den