Which contraption is used to temporarily restrict blood flow during a blood draw?

A tourniquet is the contraption that is used to temporarily restrict blood flow during a blood draw. Its primary function is to engorge the veins, making them more prominent and easier to access for the healthcare provider taking the blood sample. By compressing the tissues and veins in the area, the tourniquet creates a temporary barrier to venous return without affecting arterial flow too significantly. This helps streamline the blood collection process and minimize discomfort for the patient, facilitating a successful draw.

The other options serve different purposes: a scalpel is a surgical tool used for cutting; gauze is often used to absorb blood and promote healing post-draw; and forceps are used for grasping or manipulating tissues or objects but do not restrict blood flow.