Abstract: A cutter blade is pivotally attached to a blade carrier so that it may operate as a flail. The blade carrier itself rotates about a drive shaft spaced from the pivot axis. A pivot pin is received in respective bores of the cutter blade and the blade carrier; a distal, protruding portion of the pivot pin is threaded. A pair of clamping collar halves each have a threaded surface which threadedly engage the threaded portion of the pivot pin shaft. After the correct amount of axial play between the cutter blade and the carrier is adjusted by rotating the collar halves on the shaft threads, the collar halves are clamped together on the pivot shaft using fasteners so as to affix the clamping collar halves to the shaft.