Billet Metering Block Standard Calibration fits most 1850, 3310, 4776, 4777, 4778, 4779 Holley® model numbers. Has spark advance provision. Our billet aluminum metering blocks are machined to very strict tolerances then anodized for protection and good looks. CNC cut from premium aluminum and filled with precision parts, these blocks provide the ultimate platform for your performance carburetor. Standard calibration for out of box performance - designed to fit most real world street & strip carburetors. Simply add your jets and power valve to complete the installation. Our billet aluminum metering blocks are machined to very strict tolerances then anodized for protection and good looks. CNC cut from premium aluminum and filled with precision parts, these blocks provide the ultimate platform for your performance carburetor. Standard calibration for out of box performance - designed to fit most real world street & strip carburetors. Simply add your jets and power valve to complete the installation.