Vintage Barbour Stockwell RPM / Tachometer gauge.  Quality vintage USA made, they are heavy gauge chromed brass.   Bezel measures approximately 9" across or so with a glass front.  They were found among the collection of a retired machinist.

These are NOS, never used.  Not perfect, but probably as nice as you are ever going to find.

There are other versions of these once in a while on ebay.  You could take this apart and make a different face plate for some other measurement / style.  


Please ask any questions first.  There are 3 available, two of them are still in the original boxes with padding, and the other is loose.  Let me know which you want at time of purchase.  

I am not the original owner of these and have no way to try them out so being sold as found.

Good Luck