What is this

Still learning to paste photos. Patience please.

 

You are doing great with the photos!

It looks like an adapter to your speedometer cable. I guess a regular one wasn't reading accurately?

 

I agree with Paul. It'll have a gearset inside to correct speedometer error.

 

Speedo Correctiion Device

Once in a while you'll find one of these with a lever on the side , it's for trucks equipped with two speed rear ends .