Pre-drilling oak for screws

25 Feb 2015
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United Kingdom

I'm building an oak bench and will pre-drill and countersink the screw holes. If I have number 4 screws what size bit should I use? The same size or smaller? Thank very much for your advice.

Competent DIY-er.
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Maybe you could peg or dowel it

Traditionally, square oak pegs are hammered into round holes.
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If you screw it, pilot and countersink the holes (3.2 to 3.5mm - I think 3mm is getting near to the point where you can snap a 4mm screw off in oak, but would be OK in softwood) then screw the parts together using lubricated steel screws, the same size as the final screws you will be using (use tallow, wax or soft soap from the bathroom as a lubricant). This cuts a nice neat hole for the finish screws to use

When complete, one at a time back the screws out and replace with identical brass or stainless steel screws. As others have said - ordinary steel screws corrode in oak, stainless and brass don't, but they are very soft and can snap off or the heads burr out if over torqued, hence the long winded approach to installing the final screws
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After piloting, just candle wax the non ferrous screws and don't use an impact driver or high torque cordless, hand screw only.

But if possible, bolts may be better to deal with any movement in use.
Thanks everyone for your help. I'll use carriage bolts for the legs and try your advice for the various slats.

Have a great weekend!

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