5 there is shown the lockpin 16 which has a cylindrical body portion 46 with a front end 40 and a rear end 42 the rear end 42 is preferrably configured as bayonet shaped with at least two radial projections 48 an opening 44 is disposed in front end 40 and is adapted to receive a wrench or other tool not shown used to rotate the lockpin 16 in a preferred embodiment the opening 44 has a non circular hexagonal operating portion rotation of the wrench after its insertion into the opening 44 by an operator serves to rotate the lockpin 16 the lockpin 16 extends through bore 24 in the cutting head 12 and may be attached to the cutting head 12 by any suitable means in the embodiment shown in fig1 a circular groove 41 is constructed in the lockpin 16 near the middle of the lockpin 16 a clamp 45 is disposed in the shank 14 such that it secures the lockpin 16 by means of fitting into the groove 41 in an alternative embodiment as shown in fig6 a circular groove 47 surrounds the front end 40 of the lockpin 16 and a pin 43 is disposed in a bore 39 within the cutting head 12 perpendicular to the longitudinal axis of the cutting head 12 in order to secure the lockpin 16 in the bore 24 in a like manner the pin 43 extends into.