This object is called a "knife head." It& #39;s a sickle mower part. Parts like it in function are still parts of modern farm machinery including even the most expensive combine harvesters.

It has a ball on one end, which forms the ball part of a ball and socket joint which is necessary to move the knife back and forth.

Just as an example, here& #39;s part of a sickle knife with knife head, different, newer design. This one fits a Case-IH combine.

This tweet was supposed to go on this thread. Some days Jeffie don& #39;t do so good. https://twitter.com/homemadeguitars/status/1267190224003780610?s=19">https://twitter.com/homemadeg...

Here& #39;s a video of the mechanism. The little wheel at the front, driven by the mechanism, is what drives the knife reciprocating action. https://youtu.be/ag73haWswfk ">https://youtu.be/ag73haWsw...