Pilot hole size for M5 coach screw?

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disco_monkey79

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Hi

Is there a rule of thumb for coach screw pilot holes? I've not used them before, and will be putting them in to well-seasoned oak.

I have drilled umpteen pilot holes for regular screws, but these aren't as sharp as "normal" screws.

Thanks
 
Pilot hole should be the size of the shank, the non threaded portion of the bolt/screw..
 
find out the diameter of the inner circumference ie the valleys of the thread and drill that, then the coach/lag screw will do the rest

edit as I deleted a needed bit
 
Last edited:
The threads on Coach screws are pretty course and into oak you might struggle a little so as was said above plus a bit, it can also help to drill the hole twice just to enlarge it a fraction, a bit of candlewax on the threads will help as well. Ian
 
I had to look up coach screws, and learned these are what I know as lag bolts. I was taught to drill a lag bolt pilot hole one half of the external diameter of the threads for soft wood, and three quarters of the diameter for hard wood. For wood screws, I was taught to drill the pilot hole the same diameter of the screw shaft between the threads.
 

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