Thanks Graeme I will look into it. 
Keith, I found a mob that make them, I did some research because I need some for when we build a C15A rear body.
RAGEEM Fasteners, weld on cage nuts
3/16, 1/4, 5/16, 3/8 or 5, 6, 8, & 10mm 
the cage is slightly different the way it is made but it still has the weld on tags the same length, there is a little picture of them on there web site. 
http://www.rageem.com.au/Products/Sp...peed_nuts.html 
$55inc for a box of 100 they make to order so allow 2 days,
(02) 9599 3132 
I got a stack of them I "borrowed" from the oil refinery when I was working there, I drill a hole in the tag and weld it on through the hole so it looks like a spot weld.
Jeff