How to tell the difference between a Singer 15-30 and Singer 115
Looking at a Singer 15-30 and a Singer 115 in their base or in a cabinet the two machines are almost impossible to distinguish between the two models. Both models came with different decal options and both came with scrolled and un-scrolled faceplates.
The 115 has three holes in the deck, and the 15-30 has only two. The third hole in the 115 is for the coil spring underneath the deck (see photos below).
From below they become easy yo tell apart. The shuttle area is quite different, and the Singer 115 has only one rocker bar and a coil spring isn’t found on the 15-30.
You can see the hook race of the 15-30 if it’s just sitting on a table.
Side note: The 15-30 uses a 1:00 bobbin case with a class 15 bobbin, and the 115 uses a 206 or 306 Swing-Needle bobbin case with a class “L” bobbin
