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I have a M6 x 1 hollow threaded rod, which I want to screw into a metal block (which I obtained from an old dysfunctional machine of the same type). The metal block's hole (its an un-threaded hole) in which the threaded rod is suppose to fit has 7.85 mm inner diameter.

I was thinking of using helical inserts, but the product's outer diameter is 7.95 mm which is slightly bigger than the metal block's hole, but nonetheless makes it useless in terms of tapping metal block's hole. My application requires that the part work properly up to a temperature of 300 F. Is there any way to do this without having to completely machine a new metal block?

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Sure. You tap (or drill out and tap) the larger hole for a convenient thread size, and use an M6 threaded insert with that thread size (from personal experience, I suggest not using the helical type unless you have to - if there is no space constraint, a larger-outside-thread solid insert holds up better.)

M6x1 with an outer of M10x1.5 seems to be a common solid insert size that should work with the constraints you've mentioned, in "drill out and tap" mode.

If you have a different mindset or set of tools, you can also weld the existing hole up, redrill and tap for M6 - most folks don't go there first, as getting a good fill on a small hole is tricky - but again, you can drill it out larger first if that is the problem, or drill it out larger and weld in a plug.

  • Thanks a lot, do you know where I can buy those. It looks like McMaster carr don't have them. – user3746381 Aug 31 '15 at 22:20
  • @user3746381 yes, they do, actually. In stock even. 90240A225 for instance, and several other versions. "standard threaded inserts" "for metal" "internal thread size = M6" - 4 types, more than 4 different products. McMaster's search engine is quite effective; you can go to Enco or MSC if you'd like a bad search engine on a metalworking website, last I tried them. Might be I typoed the outer thread pitch in the answer - looks to be M10x1.25 on most of them. – Ecnerwal Sep 1 '15 at 2:01

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