The only real change is the sharpening stone he has in a pouch on the sheath. In First Blood, it is a rectangular prism, and in the second movie, it is a square steel stick. Although the first two knives were essentially the same but with minor differences, the last two movie knives have become completely different, unique designs. In the third movie, he carries a Bowie knife with a few serrations on the top, and a laminated wood handle. In the fourth movie, he carries a small handmade machete.