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Powers 5-piece 3/8 inch vs 1/2 inch

Original Post
Taylor Krosbakken · · Duluth, MN · Joined Nov 2008 · Points: 668

Some questions on the differences between 1/2 in and 3/8 in 5 piece expansion bolts.
 
So here is what I have concluded, tell me if I am wrong.
 
1/2 inch bolt advantages:
Stronger
Does better in softer rock because of a less concentrated force.
 
3/8 inch bolt advantages:
Cheaper $7 (compared to $14 for 1/2 in) still about the same as a glue in.
Smaller hole to drill (faster)
Strong enough
 
So looking at the strengths of these bolts in different strength concretes, the 3/8 in bolts lose almost half their strength going from 41 MPa compressive strength concrete to 14mpa, while the 1/2 in only goes down 20% in strength. Concluding the 1/2 in do better in softer rock.
 
Now the only rock I could find even as low as 20 MPa compressive strength is mudstone, with most sandstone, Dolomite, Limestone being at least 40 MPa compressive strength. So in most rock you are comparing 38.9 kN to 55.4 kN and 3/8 in are plenty strong.


So are all of my assumptions correct? Is the only good reason to use the more expensive 1/2 in bolts if you are bolting really soft rock? I think I have also seen using 1/2 inch bolts on a crux bolt that sees repetitive whips. Is that even necessary?

What am I missing? The funny thing is, I got some 3/8 in 5 -piece bolts in the mail, and I thought they looked teeny tiny, but the published data sure makes em sound plenty strong.

Thanks!
Bruce Hildenbrand · · Unknown Hometown · Joined Apr 2003 · Points: 1,220

3/8" 5-pieces are plenty strong.  We use the 3.5" ones at Pinnacles National Park for rebolting.  The rock quality there is a bit suspect and we have to hand drill so that is a good bolt for us.

Taylor Krosbakken · · Duluth, MN · Joined Nov 2008 · Points: 668

Ya I assume hand drilling 1/2 in would be terrible. That would be a good reason to not use them, but luckily I do not have to hand drill anywhere I am bolting. 

Matt Z · · Bozeman, MT · Joined Mar 2012 · Points: 170

You probably already know this, it's worth repeating for the masses:

The new Powers PB+ plated bolt in 3/8 is not suitable for climbing applications. The 304SS Powerbolt in 3/8 is suitable. The inner bolt on the new PB+ is only a 1/4" bolt.

Besides that minor detail, SS 3/8" sleeve bolts are fine. Most (certainly not all) 1/2" bolts are used for replacement of 3/8" and it makes sense to drill the hole out to 1/2" after spinning the old bolt and wallowing out the hole a bit. Bolt replacement is also another reason to consider using a 3/8" initially as the hole can get widened to 1/2" when the bolt reaches the end of its lifespan to take either a glue-in or a 1/2" sleeve.

Taylor Krosbakken · · Duluth, MN · Joined Nov 2008 · Points: 668

Yup. I am talking all stainless here. But a good reminder M Z.

Looks like the PB+ plated bolt in 3/8" are rated to 17.7 kN. Which isn't insta-death, but for a modern bolt is pretty poor.

And good thoughts on replacement.

Brandon Fields · · Boulder · Joined Apr 2016 · Points: 500

If you’re working with decent stone and are putting in a new route, I’d reach for the 3/8in almost every time. I’m a proponent of starting with a smaller hole to extend the life of the hole if it will be rebolted or to have as little impact on the rock as possible if it is never climbed again. The benefit of saving tons of money is just icing.
I’d save the 1/2 bolts for rebolting, bad stone and high traffic cruxes.

Timothy Fisher · · Unknown Hometown · Joined Nov 2017 · Points: 0

I think the 25kn standard is a good one. High quality 3/8 bolts are right there. I only use the Hilti KB3 wedge and of course the Powers 5 piece in 3/8. Goes without saying SS.

Ordinary stainless wedges in 3/8 do not satisfy my idea of a good permanent anchor.

For softer rock bigger is the right thing to do.

Matthew Fienup · · Santa Rosa Valley, CA · Joined Feb 2006 · Points: 7,296

In 2007, Fire Crags in Santa Barbara, California, suffered its second failure of a 3/8" x 3.5" five-piece sleeve bolt. The bolt pulled out of the wall during a routine lead fall. The sandstone at this particular crag is among the softest on the Central Coast, but the bolt failure was still surprising. 1/2" sleeve bolts are the standard for sandstone routes on the Central Coast.

I would encourage you to treat the numbers in the Performance Data table as a best case scenario. The density of rock at many climbing formations, especially sandstone ones, varies dramatically over space. Moving a bolt four feet might yield a placement in rock that is 50% more dense. Also, the quality of the holes drilled in the field is likely to be much lower than in a testing environment, resulting in very different pull out strengths.

Ward Smith · · Wendell MA · Joined Apr 2009 · Points: 295

If you are using a power drill then there is no reason not to use a 1/2 inch bolt other than cost.  I'm using mostly 1/2 inch wave bolt glue ins in hard rock (gneiss) and 1/2 inch power bolts only rarely.  Been bolting for 30 years, and the 3/8 stainless I put in long ago are still mostly good in hard rock but they do end up spinning and eventually need to be replaced.

Nick Drake · · Newcastle, WA · Joined Jan 2015 · Points: 637
Ward Smith wrote: If you are using a power drill then there is no reason not to use a 1/2 inch bolt other than cost.  I'm using mostly 1/2 inch wave bolt glue ins in hard rock (gneiss) and 1/2 inch power bolts only rarely.  Been bolting for 30 years, and the 3/8 stainless I put in long ago are still mostly good in hard rock but they do end up spinning and eventually need to be replaced.

I agree with your sentiment and think that's best practice. One exception I can see to not go right to a 1/2" glue in is if you're not 100% sure of the best location for a clip it's easier to remove and enlarge or patch the 3/8" hole later. For something that's steep enough that running it on TR is tough for some reason that might be a consideration. 

JD Borgeson · · Little Rock, AR · Joined Apr 2013 · Points: 1,190

I've so far gotten two responses on my most recent thread in regards to the Powers SS 3/8" that say this "Nobody should be using 3/8ths these days unless you are super out there and need to role extra light.
The sleeve on the 3/8ths five piece is like a soda can in quality at least use 3/8ths wedge bolts or even better just dont use 3/8ths its 2020."  This is a quote, and there is another user echoing the sentiment.  This thread and my thread seem to be completely at odds, so what do you guys say about this statement?

Timothy Fisher · · Unknown Hometown · Joined Nov 2017 · Points: 0

I have stainless 3/8 5 piece that are 30 years old at several different crags in NC and WV. They are not spinning or otherwise needing replacement. I dont buy the idea that 3/8 it not good enough in hard rock. Many of these bolts were upgrades of 1/4 inch bolts.

Adam Beach · · North Conway, NH · Joined Jun 2013 · Points: 28

I’m curious about the idea of 1/2 vs 3/8 in bullet granite, assuming they rust at the same rate. Say they each lose a little bit of circumference due to rust, the 1/2 inch would be a little stronger in shear, but wouldn’t they both lose mass relative to the hole size resulting in a similar loss of pullout strength and then also negate the 1/2 vs 3/8 argument? If someone has a better way of phrasing this please do so, im having a hard time wording it. Does that make sense to people?

Josh · · Golden, CO · Joined Jan 2006 · Points: 1,070

I started out placing mostly 3/8" Powers 5-piece SS bolts (since I was placing in hard rock and they were cheaper) and 2 years ago bought a batch of 1/2" ones instead (because I was not hand drilling, and they were on sale).  I have generally read/heard the same as you:  the new SS Powers bolts of both diameters are still strong enough, and in hard-enough rock the 3/8" diameter is often adequate.

The torque specs for the two diameters are different, and in my experience the 3/8" was a bit harder to get just right, and perhaps for that reason, among my first several routes installed with the 3/8" bolts, several loosened quickly and needed retightening.  It is not, of course, completely unusual for any bolt to need retightening after some amount of initial use.  But in my own experience, the 3/8" ones seemed to want to loosen more often, and since then I have heard others say that the 3/8" stainless in particular are more prone to that.  That alone wouldn't dissuade me from using a 3/8" bolt in the appropriate setting, but just something to be aware of.

Two years ago, when I bought the batch of 1/2"ers and started placing them, I thought (kinda like what Ward Smith said) I wouldn't have much reason to return to 3/8" (other than what Matt Z and Brandon Fields said about bolt replacement).  But that was before the tariff war-- now I look online, and the 1/2" bolts are PLENTY more expensive.  I might have to start a GoFundMe for my next route...

nbrown · · WNC/Broomfield, CO · Joined Nov 2007 · Points: 7,000
Adam Beach wrote: I’m curious about the idea of 1/2 vs 3/8 in bullet granite, assuming they rust at the same rate. Say they each lose a little bit of circumference due to rust, the 1/2 inch would be a little stronger in shear, but wouldn’t they both lose mass relative to the hole size resulting in a similar loss of pullout strength and then also negate the 1/2 vs 3/8 argument? If someone has a better way of phrasing this please do so, im having a hard time wording it. Does that make sense to people?

I may be wrong, but I think the 1/2" bolt, by virtue of the larger circumference, would still produce more friction and thus have a higher tension/pullout strength.

Timothy Fisher · · Unknown Hometown · Joined Nov 2017 · Points: 0
Adam Beach wrote: I’m curious about the idea of 1/2 vs 3/8 in bullet granite, assuming they rust at the same rate. Say they each lose a little bit of circumference due to rust, the 1/2 inch would be a little stronger in shear, but wouldn’t they both lose mass relative to the hole size resulting in a similar loss of pullout strength and then also negate the 1/2 vs 3/8 argument? If someone has a better way of phrasing this please do so, im having a hard time wording it. Does that make sense to people?

So i would answer flatly that non stailess bolts should not be a consideration anywhere in the east. If cost is your primary concern use a SS wedge from team tough or hilti.

Adam Beach · · North Conway, NH · Joined Jun 2013 · Points: 28
Timothy Fisher wrote:

So i would answer flatly that non stailess bolts should not be a consideration anywhere in the east. If cost is your primary concern use a SS wedge from team tough or hilti.

I use the 10mm / 12mm team tough, always stainless. I assume that even stainless will rust eventually, which is what my question was about. Should have been more specific in my post. I would say non stainless isn’t any option anywhere, not just the East.

Kent Krauza · · Vancouver Island · Joined Dec 2018 · Points: 0
nbrown wrote:

I may be wrong, but I think the 1/2" bolt, by virtue of the larger circumference, would still produce more friction and thus have a higher tension/pullout strength.

The 1/2” bolt has 1.78 times the cross sectional area of the 3/8” bolt, and the shear strength is proportional to this, all other things being equal.  As far as holding power, the distance that the wedge drives the sleeve into the rock (expansion distance) is larger than that of the 3/8” bolt, the difference this time being the ratio of the diameters, so only 33% more.

nbrown · · WNC/Broomfield, CO · Joined Nov 2007 · Points: 7,000
Kent Krauza wrote:

The 1/2” bolt has 1.78 times the cross sectional area of the 3/8” bolt, and the shear strength is proportional to this, all other things being equal.  As far as holding power, the distance that the wedge drives the sleeve into the rock (expansion distance) is larger than that of the 3/8” bolt, the difference this time being the ratio of the diameters, so only 33% more.

Not sure if this answers Adam's hypothetical question upthread; that's all I was trying to do. 

Also, are you sure the relationship between "expansion distance" and "holding power" (I guess you mean tension?) is a linear one? May be, I just don't know.

Adam Beach · · North Conway, NH · Joined Jun 2013 · Points: 28

gotcha, so by virtue of the larger diameter, you have a larger margin, that makes sense. The question kinda gets into the weeds quick. Like let’s assume you could re use the holes, I would argue that high quality 10mm or 3/8 first then boring the holes to 1/2 is the most environmentally friendly (wouldn’t that be the ultimate litmus test)? Thoughts?

Timothy Fisher · · Unknown Hometown · Joined Nov 2017 · Points: 0

Hey Adam sorry when you said rust i thought ferous hardware. I think the better word for 300 series stainless would be corrosion or SCC.

I dont think "bigger" helps much with SCC. In hard rock 3/8 diameter has abundant strength safety factor. So the question is can SCC be a factor in the location. Rock type. Sea cliff. Climate.

From several 28 to 30 year old SS 5 piece bolts i have recently inspected in NC, I am confident there is no one currently alive who will need to replace them. 

Guideline #1: Don't be a jerk.

Fixed Hardware: Bolts & Anchors
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