This is an individual Kluson tuning key from an incomplete set.  Has Patent #.  BASS-SIDE!  It is the 3x3 style, but NOT the 3-to-a-plate style.  The most obvious fit for these is 60’s Rickenbackers and Martins.  

Gibson used the same format Kluson keys on several guitars (ES-330, Southern Jumbo, Country & Western, to name some), but in my observation those always had plastic buttons; these are metal.  (Gibson also used a lot of 3-to-a-plate keys, like on J-45’s and J-50’s, also with plastic buttons.  Keep in mind that Kluson supplied tuning keys to a LOT of different companies, especially in the 60’s, to include Gibson, Fender, Martin, Rickenbacker, Supro/Airline, and MANY others, so this may fit many other models.

Listing is for one tuning key only; does not include the bushing or mounting screws.  Please review the pictures and hit me with any questions.