Floats for Holley 2-bbl and 4-bbl performance carburetors come in two basic designs: side hung and center hung. A side hung float is so-called because the float arm is attached to the side of the float and it is hung or pivoted from the side of the float bowl. A center hung float has its float arm attached to the float center and its hung or pivoted from the center of the float bowl.The float material used in any particular carburetor is very often dependent on the carburetor usage. For example, carburetors designed to run on alcohol must use a brass float: carburetors set up for blow-through forced induction systems need to use nitrophyl floats; carburetors used on a draw-through forced induction system could use either a brass or a nitrophyl float. Today, Holley float designs are manufactured in only brass or nitrophyl, and they are interchangeable, except on secondary 4160 w/brass center hung floats. Most Holley performance carburetors have externally-adjustable floats. This feature greatly facilitates ones ability to help keep the carburetor in perfect tune.