According to the Idiot’s Guides, the function of the thread take-up lever is to pull thread from the part of the sewing machine known as the spool and to feed this thread through the machine. The lever is made up of the thread guide and the metal finger.
According to IFixIt, the thread take-up lever forms part of the threading system of a sewing machine. The take-up lever is positioned above the presser foot. The take-up lever lifts thread up and out of the material after a stitch is made. Take-up levers are also gauges that show the needle's position.