Do you have one to compare them to a standard Holley mixture screw out of a regular 4 barrel carb. like the early List # 1850 carbs? If not try calling the The Carb Shop, 909-947-3575 and ask them if they have them or not I've never tried comparing the two against each other but it wouldn't suprise me that Holley kept them the same If not try calling the Corvette Shop in Chicago, IL they (sorry, no phone number for them now ) may have some left also They bought all the surplus sixpak two barrel carbs parts from Holley a lot of years ago Good luck