extension 3 the main shaft 1 as depicted has two diametrically opposed keyways for engaging with co operating keys formed on and internally projecting within the arbor extension 3 furthermore the arbor extension 3 receives two sets of aligned arbor locking screw caps 4 that when fitted are recessed within the outer external surface of the arbor extension to avoid interfering with fitment of the blades and spacers the arbor locking screw caps 4 are located within the keyways of the main shaft 1 to locate the main shaft 1 and the arbor extension 3 the arbor extension 3 has an internal wall not shown through which the end locking bolt 5 projects to engage and retain the end of the main shaft 1 the main shaft 1 is thus firmly locked to the arbor extension 3 via use of keyways cap screws 4 and the end bolt 5 as can be seen the main shaft 1 u2014 which does not form part of the grinding attachment per se u2014 is depicted in partial view only as the housing and ancillary equipment to which it is attached is of no further concern typically the main shaft 1 would be driven by an industrial diesel motor mounted on the highway grinder the blades and spacers are retained on the arbor extension 3 by use of two internally threaded.