A New Bolt

I've seen lots of bolts and nuts, but I just found a new one.

This is a square headed flat head bolt.  It is a 1/2-13 NC bolt.  They came off my old sickle bar mower project - they hold the long bar plate to the shoe.  I'm sure they have never been taken off, at least in the last 50 years.  Threads are a bit thin, but I'm amazed at that tapered square head.

And I'm even more amazed at the mating plate that it fits into.  As a wanna-be machinist, I'm not too sure how they made that tapered square hole for the bolt to sit in.  I've never been able to make square inside corners, let alone on a taper.  I don't know how they did this 65 years ago.

I thought about trying to take a standard hex bolt and make some new bolts of this style, but I don't really know where to begin.  I think I'll just clean up my old bolts and hope they don't break when I torque them down.  

Neat stuff.