It looks like a Singer Model 20. The number of spokes in the hand wheel changed over the years, and is the best indicator of the approximate age. The pad on the base is another age indicator, as is the material that the hand wheel is made out of, and whether or not the thread guides are numbered. The box is also an age indicator, if it can be determined that it is in fact the original box for that machine, as it changed through the years as well. Yes, they came with a “C-clamp” to clamp them to the edge of a table or board to stabilize them.
I have a 1914 Singer 20-1 Type 2, from what I can determine. It has an 8-spoke nickel wheel, no thread guide numbers and no base pad. My clamp is missing the pivot cap on the end of the screw.
CD in Oklahoma