Holley alcohol jets are specially designed to work only with the following model
4150 HP carburetors: 0-80542 (650 CFM), 0-80535 (750 CFM) and 0-80498
(950 CFM).  THe unique metering blocks used with these carburetors are
designed to accept the physically larger size of this main jet. 
There are two (2) jets per package. 

Installation Notes
Fits Holley Models 4150HP and 4500HP Originally Designed for Alcohol.
NOT FOR GAS CARBURETORS CONVERTED TO ALCOHOL.

Part # HOL 122-132