This is the brass bushing that goes in the head to reduce the size of the threads to accept the fitting for the temperature gauge. Tested to fit correctly on our 216ci display... For 1938 1939 1940 1941 1942 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 Chevrolet Cars and Trucks