This is the sending unit that measures the amount of gas in your tank and relays the information to your gas gauge. Brothers sending units are constructed of high quality stainless steel. Fits the below applications blazer - 31 gallon tank73-77 250ci1977 305ci (2wd)1973 307ci73-77 350ci (75-77 2wd or 4wd with manual trans) suburban - 31 gallon tank73-77 250ci1973 307ci73-77 350ci (manual trans) suburban - 40 gallon tank73-77 250ci73-77 305ci (manual trans)1973 307ci73-77 350ci (manual trans)