I saw this machine's listing and it turns out the seller lives in the same general area as a possible house I was to look at and so I contacted him. This is a German Singer zig-zag made in Karlsruhe and is most closely similar to a 306, although it has several advantages: uses class 15 bobbins and needles, has feed dog drop on the bed, and the slide plate actually slides. It's also built to tighter tolerances and so it's quieter and smoother (although not by so much that the difference affirms the silly, ignorant maligning of the Swing Needle machines -- the 206, 306, 319/320). Like the 306, it has adjustable needle position and takes cams for decorative stitches. It weighs in over 50 lbs.
My machine came in a wood base but lacks a case. Additionally, the lamp shade is missing and the lamp socket housing is cracked. I have ordered a vintage lamp but it is black, so I'll either have to paint it or be satisfied with it as-is. By the way, these lamps are quite expensive. Luckily, I found one in Germany for just $17 plus shipping ($9) but all the other sellers had theirs well over $50 and higher. They're not rare, just expensive.
Although this is a Singer, the Germanic pedigree is evident immediately in its sewing characteristics. The machine runs beautifully; I can see why these are such coveted machines: quiet, strong, adjustable down to the slightest differences in width and length. I love the styling, too -- reminds me of the 15-125, for example. One question I always ask myself when I acquire yet another machine is whether I plan to keep it and for how long. The 316 will be in my permanent collection.
If you find one of these beauties, don't hesitate, especially if you can find one for well under $100 as I did. You'll be glad you bought it!
