What is this? A Key?

[annaques]

This looks like a key on the top but the shaft is grooved.  Thank you in advance.

[mr_lincoln]

@annaques   The shaft is threaded (like an ACME thread) and the ball at the end would fit in to a socket.  Something would be on the thread and move back and forth or tighten .  It appears to be an early version of a "ball screw" ...

I'm not sure how long it is but the screw thread appears to be a course thread opposed to a fine thread. 

[annaques]

Overall it is 4 1/4" long and the threaded portion is 3 1/2" long

[mr_lincoln]

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@annaques wrote:

Overall it is 4 1/4" long and the threaded portion is 3 1/2" long

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@annaques   Thank you for the dimensions ... it could have been part of an antique jewelers vice or clamp.

[mr_lincoln]

@annaques   I took these pics of one of my bar type clamps.  This will help visualize how a piece like yours would work ...