I have had thousand of Craftools pass through my hands over the years.  I had noticed that many of the older Craftools would have a light ring of oxidation around the shaft just behind the toolface.  I had pondered the reason for this often.  I wondered did maybe the chrome plating have fine cracks in it caused by stresses in the metal, perhaps from the pounding these tools take.  The one day while looking through an old catalog a picture caught my eye.  It showed a string of Craftools being removed from the plating bath.  All of the tools were strung on a wire which was wrapped around each tool at the same point where I had observed the ring of oxidation.  After consulting some books and talking to an old timer who used to work in a plating shop, I now believe that the "Ring Around the Collar" is caused by a weak spot in the plating resulting from the process used in those days.  Some of the older tools that were in a high humidity area would develop these rings over the years.  Living in a fairly dry area myself I had not seen this untill I started buying tools from other "wetter" parts of the country.  If you do live in one of the high humidity areas, I have heard that using Rain-X to coat all of your steel tools is not a bad idea.  You can find it in the auto section at most stores as it is a micro-crystaline wax used on windshields of cars.