Hi Norm and all, I'm not disagreeing about heavy duty mowers the base on the Hercules is 4mmm to 5mm thick, just pointing out they don't always weigh a lot more.
I have a Husqvarna mower and the base is 4.3mm thick .
I agree most of the mowers are steel or thin cast alloy bases these days.
Husqvarna advertise certain new models as having a heavy duty base. The old price it says is $1,520. you do get self drive though and a 20.8 inch base. Not sure how thick the casting is on the new Husqvarna.