That's a great find -- any chance you can go back and look for more of those? It's an early threaded piece. The initials LAC are for Louis A. Cauvet, who patented the threaded pinhole on July 25, 1865. There's some speculation these were made by Beaver Falls Glass Co. in Pennsylvania.
Unfortunately, the condition of yours will really affect the value. In very good shape, it's around a 150.00 piece, but with the surface dings and looks like a dome fracture in yours, I'm afraid that knocks it down to about 50.00.
That is a winner young man, worth $125 + in EXCELLENT condition but I see some potential problems with condition. Better, close up pix in natural / sun light would help make for a more accurate appraisal. At least you know you should be careful, persue additional input before trading or selling it.
Insulator collectors are not generally as picky as bottle collectors when it comes to condition but we still want them as nice as possible. Check it out.