THIS IS A DOUBLE GROOVE CRANKSHAFT PULLEY FOR SHORT WATER PUMP SMALL BLOCK CHEVYS. IT HAS THE STANDARD BOLT PATTERN TO MOUNT ON ANY CHEVY BALANCER, AND IS IDENTICAL TO THE 2 GROOVE PULLEYS USED FROM 1955 TO 1968, JUST MADE OF STEEL AND THEN SHOW QUALITY CHROMED. THE SIZE IS 7.3 INCHES IN DIAMETER