The reason I ask is because the spindle is just a bar threaded on both ends. The top collar (5) is threaded onto the spindle clockwise (normal for the direction of travel). If the bottom collar is also threaded onto the spindle, and I think it would be, and if it was threaded clockwise then the action of cutting grass and hitting rocks etc might tend to undo it and that's dangerous.
Not in this case. From the location of the discharge chute, spindle rotation is clockwise, viewed from the top. With a right hand thread on the bottom, any resistance [from grass or object impact etc] to the rotation of the collar [called a 'disc boss' by Rover] will tend to
tighten the boss on the shaft, not loosen it. The centre bolt will be RH thread also, for the same reason.
And as grumpy says, LH thread bolts are extremely rare. The only cutter deck I can recall encountering them on was the old Mobilco Heavycut self propelled slashers, which have anticlockwise blade rotation.
Unfortunately, I've already snapped the head of one of the bolts (45) while trying to undo it anticlockwise.
It's very common indeed for the bolts in blade carrier bosses [on all sizes of mowers] to rust into place, and for the heads to shear off when you try to undo them. They do get wet in service, after all.
Applying a good penetrating lube, and a bit of heat, beforehand is pretty much standard procedure for removing these. An impact wrench/driver can help too, if used with care. Even then, it's still common to need to either replace the boss, or redrill offset and tap it, after the bolts all shear.
Some metal-based anti-seize compound on the bolt threads is a very good idea when assembling them, as well. Including the centre bolt.
