Hi N1KKO,
I remember a guy who helicoiled my spark plug hole in the cylinder head using grease to catch metal shavings as he tapped it. I wish I had filmed it as I can't recall the exact method. I imagine the grease in the spaces of the tap will be effective in catching the shavings and holding them as it cuts a thread. What few if any fall in should be able to be flushed out with petrol or physically vacuumed out.
Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!
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