I found this pair of cufflinks browsing through a website called Uncommongoods.
Each set of cufflinks is made from authentic date nails in use from 1897. In order to record the date of construction, these steel markers were used for railroad ties, bridge timbers, utility poles, mine props, and other wooden structures.
In order to turn these historical pieces into quirky shirt accents, the shank is milled down to create a post-style cufflink. This set of two cufflinks are made in the USA.