G'day
NormLH threads are only used if there is an engineering
purpose.
I now suspect that rear roller sprocket tells another story.
If there is a landroll clutch (two clutches on the mower),
then that would explain a LH thread on the roller.
My guess is that a dog clutch (within the chaincase) acts
on this sprocket. This has been removed (in your image).
When free-rolling (disengaged), a LH thread would be needed
to stop the sprocket from undoing.
These are just thoughts - as I have no parts list for the A-V.
But I do have a hint - from an old eBay sale ...
![[Linked Image]](https://www.outdoorking-forum.com.au/forum/ubbthreads.php/ubb/download/Number/11306/filename/2015_08_ebay_av_06.JPG)