<font color=blue>Are they effective in hard clay, with 17 hp PTO ?</font color=blue>
I should have added that any standard auger you get with a $400 - $500 post hole digger will have a very hard time digging through packed clay. I've 'been there and done that' this past summer. Not fun since I had 185 holes to dig. I tried another auger I got from TSC. I tried pouring water in the 3" deep hole I managed to dig. Nothing worked.
I was just about to spend $200 on <A target="_blank" HREF=http://www.danuser.com/products/augers/2_inch_round_augers.htm>this</A> serrated edge auger from Danuser when we got some rain. The same packed clay soil that the Leinbach auger would just sit and spin on, went in slick as can be after some rain softened the soil. To be fair to the auger, we had a drought in our area, so the soil conditions were not typical. Of course, with clay, too much rain and the soil was too soft to set the posts. /w3tcompact/icons/sad.gif
If you have packed clay soil, and it's not the result of unusual weather conditions as mine was, do yourself a favor and get a good auger designed to dig in your soil conditions. If you have a lot of holes to dig, get a heavy duty digger, i.e., not from TSC or the low end Leinbach models. They will be nothing but frustration and in the end, after buying additional augers, additional cutting edges, you will have spent the same amount of money anyway as if you had purchased the heavy duty model in the beginning.