rubber grommet hole size

[cincydave]

How big of a hole do I need to drill in a plastic bucket lid to install the standard rubber grommet an airlock goes into?

 

[samc]

They are not all the same. Take some measurements and do a search for grommet sizes and you will see diagrams showing the ID/OD measurements. FWIW last one I drilled was a 9/16" hole. You can also just eyeball it by holding a drill bit up next to it.

 

[cincydave]

Thanks, biggest bit I have isn't going to be big enough, so I'll have to file it out.