the weight of the floor polisher at a sufficient height that the abrasive unit end of the spring does not contact the plate in normal use it is also important that the spring be sufficiently displaced by the weight of the floor polisher to maintain the abrasive unit in a substantially planar relationship with the floor it would be apparent from the description that as the abrasive unit moves vertically in response height variations in the floor the angle of the abrasive unit is slightly altered within the range of travel typically employed in the present invention the deviation from planarity is acceptable fig5 is a partial view of the variable vertical displacement mounting device of fig3 and 4 the abrasive unit is illustrated separately in fig6 the abrasive unit 4 comprises an abrasion head 16 with a frustoconical base 17 the frustoconical base 17 is received by a mating frustoconical void 19 in the holder 12 the frustoconical base allows the abrasive unit to be easily placed in the holder and yet due to surface resistance prohibits the abrasive unit from being easily dislodged the combination of a frustoconical base and a mating frustoconical void allows ease of replacement and eliminates the possibility of dust settling between the pieces dust between two moving pieces is preferably avoided since this renders the parts difficult to separate by inserting and twisting the abrasive unit is sufficiently secured in the void to eliminate displacement the abrasive.