This might be it. The link wont work but this is it. This place but the item link wont work.
http://www.midwestacornnut.com/index.html
Steel Cap Screws, Steel Bolts, Steel Nuts, Steel Acorn Nuts, Steel Washers, Steel Spacers: Midwest Acorn Nut Co: Troy, MI
Fastenal Part No. (SKU): 37983UNSPSC : 31161731 Manufacturer: Fastenal Approved Vendor Category: Fasteners > Nuts > Weld Nuts
http://www.fastenal.com/web/products/fasteners/nuts/weld-nuts/_/Navigation?term=&termca=&termpx=&sortby=webrank&sortdir=descending&searchmode=productSearch&zipcode=&filterByStore=&filterByVendingMachine=&r=~|categoryl1:"600000 Fasteners"|~ ~|categoryl2:"600072 Nuts"|~ ~|categoryl3:"600123 Weld Nuts"|~ ~|attrdiameter:390|~ ~|sattr02:^18$|~ ~|sattr05:^"Standard Hex Pilot"$|~