This 3-prong terminal block / socket fits the 221 Singer Featherweight, and many other vintage Singers including the Models 15, 66, 99, and 201. It includes the thumb nuts that connect the wires onto the back side.
These are new reproduction parts and if you are going to use it on a Featherweight there are a couple of notes. You may have to use your original thumb nut on ONE of the terminals for it to clear and mount back in your 221. Also, the threaded posts on the back are slightly shorter so you will have to compress your original ring connectors on the two wires that connect to terminal #3 just a bit to get the thumb nut to start and engage a couple of screw threads on the post. (Both of the other terminals only have one wire connection and they work fine without modification).
WILL fit the Singer 222 if you are converting the cord set to the US round-prong configuration for voltage conversions.
Will not fit the Singer 301.