No. It is the normal thread. It sounds to me it is on very tight. You will need a socket set to remove more than likely.
Rob
August 2011
We have a Champion RL534 TR and we have changed the blade this morning. It is best to use a ring spanner (ours was a 14mm) and to undo you need to turn anti-clockwise. We found the nut really difficult to undo initially (not removed for 8 years) but resorted to taking it to a local lawnmower repair man who removed it with an air gun.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix lawn mowers.