There were a few questions awhile back on making a Drill adapter that would prevent your drill asembly from falling down the hole. Here is my solution, I took a stock Nimrod adapter and had a larger washer welded just below the Drill Chuck, then had a collar made with 2 pieces of bar stock welded on and then held that in place with a roll pin.
with this setup the bars spin freely enugh that if you get in the way of one while it is spinning it isn’t going to hurt….to Bad. And I don’t have to worry about plastic or anything else breaking.