An old tool in the mill or lumber industry???????

This has been in the family probably since the turn of the century (the one before) but nobody knows what it is. A great great grandfather had a mill and an old family member said he thought it belonged to old grandpa Hunt. Would like to know if anyone knows what this is.
There are some markings on one face of the round center part that look like it could be adjustment points, and a faint stamping of Seattle, WA.