Can holes in wood studs that previously held lag bolts be re-used with lag bolts of the same diameter or will this not hold safely?

More detail: I have a piece of fitness equipment mounted to wood studs in my garage. It needs to support ~350lbs of weight. The equipment needs to be removed and replaced. Can the replacement go back into the same holes or will new ones need to be drilled? I cannot use larger diameter lag bolts since they will not fit through the mounting holes on the fitness equipment.

Possibly irrelevant: It is a Rogue 3x3 Strip used to hold a Matador lite dip station. Since the load is very heavy, I used poplar boards as stringers to distribute the load across 3 studs. The strip has 4 holes for lag bolts so a total of 12 lag bolts were used. Unfortunately, one of the lag bolts broke off in the wall as it was being tightened. It was in the middle, directly anchoring the strip. In order to get it out, I'm pretty sure I need to remove everything to gain access to the hole and extract it.

  • Why couldn't you just use the supplied 4 lags and secure to one stud? Does it say you need to use more than 4 lag bolts? I do have to say, that company has some really nice workout equipment.. – Gunner Sep 16 '19 at 18:11
  • @Gunner maybe I could've but I was a bit weary about having only one stud to support the weight. What's done is done though. – Dan K Sep 16 '19 at 18:16
  • Hello, and welcome to Home Improvement. You could just ignore the broken bolt and add a new one below it. And, you should probably take our tour so you'll know how best to participate here. – Daniel Griscom Sep 16 '19 at 19:17
  • @DanielGriscom, that's not possible. The strip has only 4 fixed locations for mounting bolts. – Dan K Sep 16 '19 at 19:51

The important thing when reusing holes for lag bolts (or screws in general) in a material that the screw will cut threads in (i.e. wood, but also applies more generally to any material much softer than the screw being driven) is to turn the bolt backwards (counterclockwise for a normal right hand thread) until you feel it "drop in" to the existing thread - then start turning forwards. That way you are following the existing thread in the wood to reinstall the screw, not starting to cut a new thread just a bit off from that one and reducing the strength & holding power of the wood.

  • Good to know! What if I cannot feel the "drop" into the existing threads? – Dan K Sep 19 '19 at 15:19

Yes, you can reuse screw holes in wood or plastic. Just make sure the new screw has the same diameter, thread pitch, and thread shape.

When reattaching, roll the screw backwards a couple of revolutions and feel for the "hop" of it dropping into the existing thread. Sometimes there's a little hop and a big hop; you want the big hop. If you do much mechanically, this should be a daily habit.

Expect insertion torque to be much lower. This isn't a metal screw; it doesn't create clamping strength by stretching the fastener shank. The torque cuts the thread initially, since screws are by nature self-tapping. There will be much less torque when the thread is already cut.

If you are snapping off threads, it's time to remember "monkey tight, not gorilla tight". If monkey-tight is insufficient to drive the fastener, then you need to pre-drill more. If you want to get scientific, consult the manufacturer as to maximum elastic torque before introducing metal fatigue, and don't exceed it. The material you're going into is irrelevant to the torque capacity of the fastener.

  • Curious if you'd keep the same opinion if the screw was being subjected to direct pull out force. If you mount say a punching bag into a beam using a screw inserted vertically directly inline with the pull of the bag, would you still think a used hole is just as good as a new hole? – Fresh Codemonger Sep 16 '19 at 21:37
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    @FreshCodemonger mostly, if you are carefully staying in the previously cut threads. If you are inadvertently cutting a new thread, then insertion torque won't be much lower, because you are mulching all the wood in the thread outer radius, and I wouldn't expect much. If in doubt, drill it out, epoxy in a dowel, and start over. – Harper - Reinstate Monica Sep 16 '19 at 22:00
  • Harper is 100% correct. using the same thread pitch and size making sure the fastener travels the same path it will have the strength the original one had. This may be more obvious in plastic where you can see the damage if not aligned by turning backwards as he suggests until they align. – Ed Beal Sep 17 '19 at 13:16
  • Excellent information, thank you! – Dan K Sep 19 '19 at 15:18

Using the existing holes should be fine, so don't worry about that. There's a few other things I'll mention tho.

The lag bolt shouldn't have broken unless it had some severe manufacturing defect. When inserting large lag bolts, you should always pre-drill with the correct sized bit. You can also lubricate the bolt with a bit of wax or soap when screwing it in to make it a little easier. Lubrication will help it twist into the hole but will not reduce the strength needed to pull it out.

Also, poplar is a very soft wood. A standard southern yellow pine stud would probably be a better choice for the load sharing.

Getting the broken lag out will be very difficult, so consider repositioning the mounting bracket slightly and starting over if possible.

  • Yes, the holes that I had pre-drilled were far to small, I now realize. I also did not lubricate the lag bolts at all. – Dan K Sep 19 '19 at 15:19
  • Do you think it is not worth trying to use an EZ-out or that sort of thing? Otherwise, I will need to drill 12 more holes in the wall and patch the 12 old holes. A lot of work! – Dan K Sep 19 '19 at 15:20
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    You could try and drill out the lag bolt, but it will be very hard to keep the drill bit centered. The other thing you could do is get a small diameter hole saw and drill around the lag bolt and remove it that way. Then fill the hole with an appropriately sized wooden dowel and strong glue. An easy-out or similar isn't made to remove bolts that are super-jammed into place like yours is. The wood is pressing on the bolt so hard that the metal failed - think about that. – JPhi1618 Sep 19 '19 at 15:26
  • Actually, "how do I remove this lag bolt" would make a good additional question (with a picture). – JPhi1618 Sep 19 '19 at 15:27
  • I'll create a follow-up question, thanks for the suggestion! I would really prefer to get the lag bolt out if at all possible but I accept that it may not be worth it. – Dan K Sep 19 '19 at 15:45

Why reuse the existing holes? Just offset it especially given one of the lags snapped and you wouldn't be able to reuse that hole anyway.

I've snapped lag screws before probably because I didn't pilot with the correct size drill bit or pilot at all.

If you did want to go up a size in lag, you could probably just drill the holes out the tiny bit extra that you need without much work and with compromising the strength of the bracket but it sounds like the easiest thing is just to offset and not worry about any of those details.

In terms of strength it doesn't sound like you are taxing the pull out strength and are really taxing just the shear and the holes being a little less tight should not affect the shear. If you were mounting something to the ceiling and the lags were being taxed in pull out then I'd be a little more worried about re-using the holes.

  • Yes, I think my pre-drilled holes were too small. Part of the problem was that the holes in the wood did not line up exactly to the holes in the wall as well, further increasing stress on the lag bolt probably. – Dan K Sep 19 '19 at 15:21

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