On Tuesday, 22 August 2000 08:00:00 UTC+1, wrote:
Are Powered Posthole borers any good?

I need to make three holes in very stoney ground.
(For 4inch poles, about 12 to 18inch depth.)
Not many holes, but not a lot of time to do the work either!
Is it worth the hire of a petrol powered posthole boring machine?

No. You're more likely to break your wrists if the thing jams.
Just go out and dig.
You need along steel bar to loosen stones etc.