Ghostface uses a modified Buck 120, which is a common eight-inch hunting knife that is used as a main weapon by Ghostface, a persona adopted by the primary antagonists of the Scream film series. It also features a blood sight beveled into the top of the blade to help break suction when stabbed into flesh and also to lighten the blade. The blade features a clip-point blade, typical of Bowie-style knives along with a blade guard.
The knives used in the film are made of aluminum with solid wood handles or metallic painted rubber blades with rubber handles, although there are prop knives that use retractible blades. In Scream 4, however, they used CGI to make the knife appear as if it was going into flesh.
The handle is made of black ebony wood with finger grooves and a curved chrome tip in the first three films. In Scream 4, however, the knife looks different. The Scream 4 version features a longer handle. The stunt knives are wrapped in duct tape and the blade has a less pronounced shape and is wider to boot, with the blood sight and blade looking more faint than usual, since they don't go as deep into the knife. The Scream 4 blood sight looks much larger than the older models and the hero knives feature a smooth wood handle.
A fun fact about the Buck 120 is that it was seen on the film posters of Friday the 13th 4, 7 and 8. The knife's appearance on these iconic horror film posters may be why it was chosen as Ghostface's primary weapon.
The Buck 120 was developed by Buck in the 1960s but was discontinued around 1992 due to complaints by hunters that the blade length was excessive.
It was replaced by the much smaller Buck 119, with a blade length of closer to five inches, rather than eight. Today, the Buck 119 lives on due to great popularity. Many fans of the series do not have the money for a Buck 120 or are unable to locate it. So, they instead get a Buck 119. The Buck 119 is quite popular with fans today.
Newer versions of the 120 can be found at http://www.bladehq.com/item--Buck-120-General-Fixed-Blade-Knife--21637 .