Wall Injectors 1 and 1/2 inch Size - Bag of 100 require a drill bit approx. 3/8in wide.
The Wall Injectors 1 and 1/2 inch Size are not designed to be used as end caps like that, they are only for use in walls to apply listed products. We would suggest leaving the tip of the foam aerosol you are using in the hole after dispensing foam then removing from the hole once it stops foaming to prevent drips/leaking.
The Wall Injectors are primarily use to create space to apply insecticides directly into wall voids, such as termiticides. We recommend contacting the manufacturer directly if you need parts for your in-wall pest system.