These come in two sizes. The "small" are for the 59 to 65 center carb. The "large" for the 59 to 66 end carbs. The "small" bases also fit all three carbs in the 57 and 58 Tri-power. When you add item to cart, you can specify the size and number.
Do look at the drop down box for the 2 - sizes available on the order page.