This 1V carb adaptor is used to install the Autolite 1100-1V (1.5" carb bore) on any late model large log cylinder head (1.75" bore). Like the stock spacer plate, it has a screw boss on the side for mounting the carb linkage. It also has a threaded hole for those who need a source for manifold vacuum, or you can cap it off with a pipe plug if you prefer. Unlike other adaptors, this adaptor is only a 1/2" thick, whcih increases hood clearance and allows the use of a thicker air filter element for increased air flow and horse power.