I'm installing an undermount sink into butcher block countertops. The threaded inserts provided with the sink require a 3/8th drill bit (according to the instructions). However, I'm not able to get them to fit even with lightly tapping with a mallet.

What is my best option?

  1. Use a slightly larger bit 15/32
  2. Use wood screw directly into the wood
  3. ??

The threaded insert before insertion.

This is as far as it inserts before it crushes the top 1/4 inch

  • I'm not able to get them to fit is not a clear description of the problem ... as a result, your questions are not really answerable ... please add a clear, closeup picture of the inserts to your post
    – jsotola
    Aug 23 at 21:23
  • The inserts might require a friction fit, so they don't turn. There fore you might need harder tapping. Can also be instructions are wrong(unlikely). Pictures are good in these cases, because there are many different types of inserts, some should be press in.
    – crip659
    Aug 23 at 21:41
  • Photos added. The first one is before inserting it. The second is as far as it will go before the top 1/4 in crushes. Most of the time a light tap will push it a bit but it will just slide right back out.
    – Ben
    Aug 23 at 22:31
  • I'd go with "Option #2" in the original question. You should be able to get substantial grip (better than the anchors) using wood screws or lag bolts directly into the underside of the wooden countertop.
    – gnicko
    Aug 24 at 1:02

I used GRK 1 1/4" wood/cabinet screws (the fancy ones with the star bit) as @Greg recommended and seems to be holding fine. Time will tell.

I drilled a small pilot hole about 1/2" in. The screws have a washer head so one wasn't needed.

  • Any particular details of the screws in question that you could provide that could, potentially, be helpful to future readers?
    – FreeMan
    Aug 26 at 11:20

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