Step 1: What You Need
D-Ring Carabiner (3-5 inch carabiners work best, bigger is better. They don't need to be "load bearing")
Hex Nut (large enough to slip into the carabiner and go all the way around. The flat sides need to be big enough to drill a 1/4in hole into)
Short Magnetic Bit Driver (The kind you'd use in a power drill)
You'll need the following tools
1/4in Drill Bit
Square or Triangle needle file (must fit into a 1/4in hole)
J-B Weld (or what ever you prefer)
Drill or Drill Press (Not Pictured)
Step 2: Preparing the Nut
Drill a 1/4in hole into the nut.
Once the hole is drilled you will need to file the hole into a hexagon that matches the bit holder.
Be patient, this takes a while. You want the hole to be as tight as possible. You should nee to use the hammer to persuade the bit holder into place.
Step 3: Attaching the Bit Holder
First you may need to grind down the bit holder until it fits in the center of the carabiner.
Use the hammer to persuade the bit holder into the hole you filed into the nut. Be careful as the nut may not be very thick on the sides and may split if forced to hard.
Also you don't want to got too far through into the nut or you won't be able to slip it onto the carabiner. If you go too far through just use a file to expand the threaded hole.
Once installed use some J-B Weld around the base to hold the bit holder in place.