Senior Tech Team
Join Date: Sep 1998
Location: Mustang, OK USA
Re: What size drill bit for 3/8-16 helicoil?
When I do Helicoil repairs, I go with the recommended drill size for steel/iron parts, and use some kind of oil for the tap, preferably cutting oil, but motor oil will work. But if the helicoil repair is to be done in an alum part, such as an alum intake manifold, then i use a drill that is 1/64 smaller than the recommended drill size. AND I USE LOTS OF LIQUID FOR CUTTING, SUCH AS WD40, to prevent galling of the tap.
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