Hi James,

I am trying to choose an impact drill (driver) that can install 10
inch Spax lag screws in pressure treated timbers. Although I would
prefer a corded model, I find very few corded models on the market. (
Am I being too quick to want to shy away from battery operated models
?)
Has anyone here actually used an impact driver to install 10 inch lag
screws and if so, which driver did you use for the job ?

You don't need an impact driver to drive lag screws. A good driver drill
will do fine.

I've driven many 6" lag bolts using my 18V Craftsman cordless drill (not
impact). It has no trouble driving bolts like this, but the battery will
limit how many you can drive. Wild guess, I'm betting I could drive well
over a dozen 10" lags with my cordless drill.

For heavy duty driving or drilling, I turn to my corded Dewalt DW246. It is
not an impact driver, but it's geared for low RPM and has a LOT of power.
It would have no problem driving lags of any size, and would likely snap
the lag or break your arms before seizing up.

http://www.amazon.com/DEWALT-DW246-2-Inch-Drill-
Keyless/dp/B00002233G/ref=sr_1_1

The DW246 isn't cheap (about $160), but it's well worth the investment.

In either case, the weak link for me has been the adapter that lets you use
a 3/8" socket in a drill. I've snapped a few of these over the years, so
make sure you have a spare on hand.

Good luck,

Anthony Watson
Mountain Software
www.mountain-software.com