A barrel nut is a cylindrical nut that is screwed into the butt of the pommel and holds the handle together. The barrel nut configuration was used by Buck knives from 1961 threw 1963. During the earlier dates Buck used leather spacers and later transitioned into Bone hard fiber spacers. The last of the barrel nuts went out during some time in '63. If you look at the bottom of the pommel you should see a pea sized circle, that is the barrel nut. It may be difficult to see, even almost invisible. Great knife.