|Hot stamp die.|
This is a block of solid magnesium (you can tell by how light it is) with the image of a truck carved (or perhaps etched, I'm not sure) into the surface. It was made in 1963 according to this quote from the seller: "The reason I know my fathers company made these and he always put the date first and the job number after that so he could always know when they did the piece. Year 1963 Job #185, hence '63185'. "
I don't know why they used magnesium for these dies.
Source: eBay seller need1have1
Contributor: Theodore Gray
Acquired: 28 October, 2005