Lag screw hole size specifications I found online suggest 15/64” pilot hole for 1/2” lag screw in softwood.

This is narrower than the body of the threaded part which appears to match my 3/8” drill bit.

Am I reading something wrong, or are the pilot holes supposed to be smaller than the body of the threaded part in softwoods?

3 Answers 3


Yes, softwood will easily be compressed out of the way and you'll get extra holding power. It's why you can often get away with no pilot holes for smaller screws. Same when driving in a framing nail.

If you're dealing with old, dry softwood (eg. existing framing in an older house), then you'll probably need to increase that hole size to something closer to the hardwood recommendation.


If you make the hole bigger than the threaded part then the screw will not grip.

The pilot hole is usually the diameter of the root of the thread and sometimes, for a bolt with a shank the beginning of the hole is taken out to that diameter.

  • The root part is around 3/8”. The thread itself is 1/2”. Pilot hole suggestions are smaller than the root part.
    – ipavlic
    Commented Jun 9, 2023 at 19:52

Swiped with Google's help...

Thinking the hole should be 3/8" for a 1/2" lag... matching your drill bit.

**Pilot Hole Sizes For Lag Bolts**
Bolt Size   Shank Pilot Hole    Threaded  Pilot Hole   
                                Softwood    Hardwood
  1/4"         1/4"                3/16"      7/32"
 5/16"        5/16"               15/64"       1/4"                  
  3/8"         3/8"                9/32"      5/16"
  1/2"         1/2"                 3/8"      7/16"

More info. here

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