Step 12: Ratchet wrench interface
I went to a local tool store that sells new and used tools. A cheap import used 17mm socket for 3/8 inch drive was one dollar. I centered the socket on the bottom of the oil filter wrench and clamped it into place with a "C" clamp. Then I welded the socket to the steel disc on the oil filter wrench. As you can see, I used a grinder to remove sharp edges and give a more pleasing look.