Diamond Calk Horseshoe Company, which was changed to Diamond Tool & Horseshoe Co. was purchased by the Triangle Corporation, who in turn was acquired by Cooper Industries.
The Diamond Tool plant was located in Duluth, MN. When Diamond was sold to Cooper they closed the plant and tore it down.
Cooper Tools is now part of Bain Capital, operating under the name of Apex Tool Group. Based in Maryland, Apex sells Diamond brand farrier tools and supplies—including horseshoes.
For enquiries, you may try to contact:
Cooper Industries:
Customer Service — 877-277-4636
Sales Support — Option 1
Technical Product Support — Option 2
Warranty Product Support — Option 3
Apex Tool Group
14600 York Rd. Suite A
Sparks, MD
Phone: +1 410 773 7800
You can chek out this Facebook page where you can find information on the relevant persons who have worked for the Diamond Tool & Horseshoe Co.