I was given a sewing machine and table.It had a manual for a 15-91. However I just looked up the serial # Z3351009, and it looks like singer didn't have series for their machine. Then I noticed that although the foot pedal says it is singer, the sewing machine has no manufacturer's name. I'll post a picture if I can figure out how. It looks exactly like a 15-91 except for decal & the serial number is under the bed of the machine instead of on the bed. Looks like a generic 15-91!