This could be called a triple drive, as the block featured 1/2-inch and 3/8-inch square sockets, plus an external 21mm hexagon 'nut'. The Clarke was simple to set up; the 38mm-wide nylon strap threaded through the loop on the drive block and pulled tight to suit the filter size - anything up to a massive 300mm. Once tightened, it turned the filter easily, damaging it slightly - but the can will be heading for the bin anyway. Great for tight spots.