Thanks jonister. After drilling the hole through the blank, I use a 5/16" spade bit to make the recess for the end caps. For those, I cut circles out of the same circuit board material that the lips are made of. Then fill in with Kwikwood epoxy putty and sand smooth. It's fast drying and doesn't shrink, plus there's no runny epoxy to creep past the end caps and into the rattle chamber. Hope that makes sense.