Hi!
I just found these bolts at mcmaster. It seems that there are vented bolts (first time I saw this).
Check this one out, it has a hole about 0.1" for air venting. Should be relatively easy to drill out to the 3mm size!
Cool thing is this is probably a standard product, i.e. there should be more sources
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www.mcmaster.com]
Or go: Fastening & Joining => Fasteners => Screws and bolts => Socket Cap Screws => Vented
