What is the pilot hole size for 12mm screw?

[janieJones123]

I am going to be starting building a half stud wall this weekend. I have a suspended timber floor with a solid oak flooring on top. I have been given great advice on what materials and hardware to use. I will be fixing the sole plate to the floor with 12mm coach screws, and was wondering what is the typical size of pilot hole for this size?

Thanks!

 

[JohnD]

you can use a pilot screw that is no larger than the unthreaded part of the screw. If you hold it up to the light you will see it.

But in softwood you can use much smaller, if it is big enough for the tip of the screw to enter, it will cut its own path. The pilot will help it run straight and reduce risk of splitting. Many people don't bother with pilots at all in softwood.

If you are fastening two parts together, for example a floorboard to a joist, you don't want the thread to grip into the floorboard, so you can drill the floorboard wide enough for the unthreaded shank of the screw to be a tight fit.

You want the screw to cut into the joist below, so it needs a smaller pilot.

If you have lots of repetitive holes to drill, you can get a special drill which cuts the pilot, the clearance and the countersink in a single action.

For example

it is much quicker than drilling three times.

 

[rsgaz]

As a general rule for woodscrews, the pilot should be 70% of the nominal diameter of the screw.

Much better to either measure it with digital calipers, or do it by eye, by holding up various drill bit sizes behind the screw, until you find which drill bit matches the "root diameter" of the thread.

 

[janieJones123]

Great, thanks a lot guys for the answers!