Though i'd never heard about this type of screw anchor before i started doing research for building these domes, they seem like a great idea, if they are suitable for your ground conditions. They are recommended for use on the playa by Bob Stahl (search this page for "ground anchors") who knows what he's talking about. (Though note that once i got out there they didn't work for me. ) He specifically mentions 40-inch anchors with a 3.5 to 4 inch helix, but there are smaller sized anchors out there far cheaper, and for a dome it's probably better to use a larger smaller anchors instead of fewer longer anchors, however of course each anchor needs to be big enough to actually hold securely in the playa. For that reason i'm avoiding the 15-inch ones (pictured top left). I will be using the 25-inch ones which are available for about $3.50 each, since that way i can affors to get plenty of them. 30-inch would be good if i could find them at about the same price. One spec i found claims 2500 pounds of holding force for the 30-inch heavy duty ones, not too shabby.
From a bit of poking around online, it looks like the only manufacturer of these things is A. B. Chance Co., but don't bother going to their website if you're looking for a place to buy their product. The only places i can find selling the anchors online (except for too-small ones for holding up soccer goalposts) are:
One tip i read somewhere said to start the anchors by digging a small hole in the surface first. I imagine that this helps the helix to bite into the ground well to start. I'll definitely be trying that.
The other tip (this one is more of a requirement) is to insert a bar or pipe through the eyelet to get turning leverage.
Update May 2004: the screw anchors have gone on to far better things than my little dome project. Here are the two subsequent owners of the screw anchors, after i gave them away (i prefer to think of it more like sponsorship :)
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