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Sterling hollow block

Original Post
Bob Johnson · · Philadelphia, PA · Joined May 2014 · Points: 98

Hello Everyone!
I am considering getting a few Sterling hollow block slings to use for prusik loops. They are sold in both 13.5" and 19" lengths. I'm trying to figure out which size to get. Does anyone have experience using these as a rappel autoblock? How does the 13.5" length work out for that? How many wraps do you get and how many wraps are sufficient? My normal accessory cord prusiks are about 17" long and I usually do four wraps around both ropes and that usually leaves me a decent amount of excess to clip back into the biner. I'm concerned that the 13.5" size would be too short unless fewer wraps are needed. And I'm concerned 19" may be too long since I usually don't extend my rappel. Which length do you all use?

Mike Marmar · · Salt Lake City, UT · Joined Aug 2013 · Points: 71

The 13.5 is perfect for a rap backup. It takes 2 wraps to grip really solidly.

evolve · · Durango, CO · Joined Sep 2013 · Points: 250

I have the smaller size, it works great as an auto block when rap'ing. I generally do two wraps but will use three if I have to clean or know I'm going to be messing with untangling rope or anything where I want a little extra security. I think anymore than three would be a total PITA unless you're wanting to treat it as a hands free backup (which I'm sure I'll catch flak for even mentioning ;)). It bites really really well, maybe my favorite piece of gear. I do extend my rappel and set the auto block up off of my belay loop.

james schaefer · · Henderson, NV · Joined Jun 2013 · Points: 10

Hey Bob,
I also prefer the smaller size.

For a happy day out at the crag, these are great. However, when I started using them in mock rescue situations, where we need to be able to trust a prusik to hold without any slip, these just wouldn't cut it. Under double body weight loads, there was a constant, slow, slippage of the backup. maybe it's just the combo of my specific rope and these... never the less...

Personal opinion.

coppolillo · · Unknown Hometown · Joined Sep 2009 · Points: 70

I've used Sterling's nylon and aramid hollow block, in the short and long versions. i find the short to be too short (for a two-wrap autoblock), as the long, sewn portion of the sling robs you of some length.

if you can find a tubular cordelette material of aramid, i think it's far, far better to make your own of tubular material, rather than a flat hollow block. grips better, more supple, and you can cut it down to the length you like. i've had a homemade one for a couple years now and love it. probably time to replace it!

anyway, good luck...

Max Forbes · · Vermont & Colorado · Joined Jan 2014 · Points: 114

I use the shorter of the two for a rappel backup. Works perfectly and I've never had issues on roped down to 9.2, including on icy ropes. I am going to get a longer one to use in instructional settings. I highly recommend using hollow block.

Trevor Gregory · · Unknown Hometown · Joined Oct 2013 · Points: 0

I have a question regarding sterling hollow block strength... I see 'SWL 314 lbs' (1.4 KN) and 'MBS 3147 lbs' (14 KN) written on mine.

So in a pinch, can I use this instead of a sewn sling to extend a QuickDraw? I know Dynix slings are rated higher (22 KN) but I have never seen 2 ratings attributed to a piece of gear before... the lower rating is of concern. As per Google, SWL is 'safe working load' and 'MBS' is max. breaking strength. Isn't the KN rating for gear usually the maximum load?

Ben Stabley · · Portland, OR · Joined Sep 2014 · Points: 171

Treavor, you're right about SWL vs MBS. I suspect SWL is required more for when these are used for professional rope work, etc, which is why you see both listed. Just a guess.

I also think the 13.5" is great for rappel backup. I use 3 wraps usually, and on my leg loop, and can sail down as smoothly and as quickly as I desire.

Scott Kleeman · · Henderson, NV · Joined Aug 2016 · Points: 5

I don't remember which size I own, but for my Sterling hollow block, I use either 3 or 4 wraps depending on the diameter and condition of the ropes. This is all for a perfect hands free rappel when cleaning, stops like a dream and glides well when I hold it open. Good luck!

Jeremy Cote · · Unknown Hometown · Joined Nov 2015 · Points: 0

I didn't like the shorter one as an auto block, as it didn't leave much room to maneuver the rope, but I think I was three wrapping it.

The longer one works great when you extend. Three raps seems about right with that length.

Solution: Get both, and keep the one that doesn't work for an auto block on your emergency biner.

Brandon.Phillips · · Portola, CA · Joined May 2011 · Points: 55

sterling hollow block... is awesome. I use the 13.5 as a backup when extending my rappel. I think i usually get 3 wraps out of it. It has greater surface area in contact with the rope, and bites better than a 5mm prussik.

CodyG · · Unknown Hometown · Joined Feb 2014 · Points: 10

Bob, I buy these in sets, 1 of each. At $12 it's only $25 total. The reason they come in two sizes is to use them in conjunction. If you're only needing one, find which you like the best, but as you can tell, it's going to depend on your application. I have used these to extend repels, ascend fixed ropes, and as a hands free backup where we were simulating a rescue and I needed to have both my hands free (a catastrophe knot below me buys some piece of mind, but I've NEVER needed it). I find they hold very well, even with just two wraps, it only has to reproduce the friction of your hand after all. I use three wraps for ascending the rope. 

Bear in mind that these DO NOT have core fibers (hollow, lol) and therefore the fibers you see are the fibers holding you up. If they're beat up, you may be taking an unreasonable chance; one that could be mitigated with $12...

CodyG · · Unknown Hometown · Joined Feb 2014 · Points: 10

Trevor, MBS is typically a minimum, you would not want to know were it's definitely going to fail...but might fail well before! The MBS is the edge at which it MAY fail. Without getting into 3 sigma and a bunch of other engineering non-sense, the minimum breaking strength tends to be a VERY conservative number. 

As far as the Safe Working Load, Ben is correct, that's a rope access thing.

To use them as a runner in a pinch seems reasonable. They have very low elongation, so should be treated like Dyneema/Spectra, but will not fail if shock loaded like those. They are only rated to 17kn, sure. Trad gear isn't that strong, and your body is definitely not that strong...once you reach those forces your going to have serious problems...

Guideline #1: Don't be a jerk.

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