3/8” to 1/2″ drill bit, depending on the size of your straw
The size of the rubber grommet you need will depend on the size of your straw. I have some fat glass straws from Strawesome, and I wanted to be sure my lids would work for them, as well as my cute paper straws. Therefore, I used a grommet with an inner diameter of 3/8″, and a 1/2″ drill bit.
However, this will vary, depending on your straw, so play around a bit.
Drill an offset hole in the canning lid.
There were some raised/jagged edges, so we pounded them down a bit. You could also file them if you wanted. However, don’t be too worried about this, because the grommet will cover a multitude of sins.
Insert the grommet, wash the entire lid assembly thoroughly, and affix to your jar.