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I need to post 60 signs, mostly going onto wolmanized 4x4 or 4x6 signposts that have been outdoors for a few years. The sign holes are sized for #12 through 5/16 wood screws or lag bolts.

However I'll be running these down with a ratchet possibly with bit holder. No AC power for a drill. Don't have a cordless. Worried about splitting the 4x4s with these big screws.

Are there screws or lags of this size that can "self tap" into softwood?

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    How near the end of the posts does the screw need to go? If it's fairly nearly the end I would not be as confident as Chuck S about not splitting a 4x4, especially one that has been weathered for a few years with the end grain uppermost getting wet and drying out repeatedly, that's a recipe for brittle wood. I would go at this expecting them to split since that's the safest option — no point in hoping for the best and only preparing for that eventuality as it'll leave you short if you face the worst-case scenario (which you're bound to in at least a handful of cases). [contd] – Graphus supports Monica Aug 23 '18 at 14:25
  • Quite a different story if you'll be driving the screws in well below the cut end, the wood within the main body of the posts (a few inches down and through the rest of the length) should be basically unaffected, practically as-new in fact, and you can treat it accordingly. – Graphus supports Monica Aug 23 '18 at 14:30
  • We will be dead center and well away from any cut ends. – Harper - Reinstate Monica Aug 23 '18 at 17:54
  • Apologies, I forgot to come back to this Question. The risk of splitting the wood is greatly lessened by the screws going in well away from the ends, but after checking what size #12 screws are I would personally prefer to still drill pilot holes because at ~1/3" the screws are pretty darn beefy. My suggestion for doing this on-site was going to be the same as @SaSSafraS1232's first paragraph. [contd] – Graphus supports Monica Aug 26 '18 at 16:18
  • A brace is the original cordless drill, only far more powerful. And with the hex adaptors available now they're brought fully into the present day, allowing one to be used with a socket bit to drive the screws after drilling the pilots. The pilots can be drilled using a traditional auger bit (this would be my preference, but finding a 5/16 one might not be easy in the time available) however some of older alligator jaws, even though they aren't built for it, can grip a round-shaft bit tightly enough to drill into softwoods. Failing that, the hex adaptor opens up numerous other possibilities. – Graphus supports Monica Aug 26 '18 at 16:25
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Drill pilot holes with a brace and bit. You'll be much less likely to split the post and you'll have a much easier time driving the fasteners. I would also lubricate each screw/bolt with some paste wax before driving it to reduce the effort required.

That said, I would seriously consider buying or borrowing a cheap cordless impact driver (though I would still drill pilot holes). Driving 120+ (2 per sign) 5/16 lag bolts by hand doesn't sound very fun at all.

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    Doing this with a brace was going to be my suggestion and is how I would do it myself if faced with the task. @Harper, re. lubricating the screws, this used to be common advice but not much recommended these days, still a useful tip to ease the driving of screws of larger diameter into wood. Other options for lubricant are linseed oil (but here, any oil will do you) or soap. If you're able to use the brace to drive the lag screws overcoming friction should be no problem at all, but if resistance builds up too high you can twist the head of the screw off. Will also ease removal later if needed. – Graphus supports Monica Aug 26 '18 at 16:40
  • If not the brace, I also have a 3/8 drive speed wrench that's pretty ideal for driving screws. – Harper - Reinstate Monica Aug 26 '18 at 17:41
  • @Harper Graphus has a good point about breaking the heads off the screws. If the resistance gets too high you can back them out and then drive them back in to help keep the friction manageable too. My understanding is that this burnishes the hole. – SaSSafraS1232 Aug 27 '18 at 16:10
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Wood screws and lag bolts of this size will self tap and will not split a 4x4. For 60 signs I would look at renting a cordless. Those posts will have dried out and will not be as welcoming to the bolts like a fresh post would be. You're in for a workout.

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