Zag Wrench Tether



Many climbers throughout the world have experimented with pairing the Petzl ZigZag and the Singing Tree ZK2 Rope Wrench (aka Zag-Wrench System) for a smooth and compact SRT setup.  Though a popular climbing technique, it's important to recognize that this pairing is not endorsed by Petzl and will void the 3-year warranty that comes with the ZigZag.

History:
Most initial efforts to pair the ZigZag and Rope Wrench utilized-shrink wrapped, cord-based, double-legged tethers.  The problem with these tethers is that they are not completely stiff and they flex when ascending the line, which leads to tending issues.  In some cases they also prevent immediate engagement of the Wrench, which puts extra strain on the ZigZag.  A number of climbers have developed rigid aluminum or stainless steel tethers such as my tether on the right.

Benefits of this Zag-Wrench Tether:

  1. The ZigZag grabs reliably and releases smoothly on just about any rope regardless of diameter of the rope, and whether the rope is clean, dry, wet, sappy, or muddy.  I've never had the Zag-Wrench system creep on me.
  2. The ZigZag will not flatten your rope as much as other mechanical SRT devices.
  3. The stainless steel D shackle that connects the tether to the ZigZag doubles as a tending point. It is low on the system which means that even climbers with a long bridge on their harness can climb efficiently. 
  4. This setup is well-suited to a rope walker foot ascender/knee ascender climbing system.  
  5. The built in swivel on the ZigZag means that the system easily resists getting twisted.  
As with any climbing system, there are pros and cons.  Here are some of the downsides of a Zag-Wrench SRT system:
  1. It is not endorsed by Petzl.
  2. It will void the warranty on your ZigZag.
  3. If the ZigZag fails for some reason the Rope Wrench will not hold the climber on the line. See discussion of this point in this video.
  4. The system is not mid line attachable.
  5. Climbing SRT on the ZigZag even with the Rope Wrench angles the ZigZag in a sub-optimal orientation that can cause extra wear on the ZigZag that it is not designed for.
Weighing the pros and cons I choose to climb on the Zag-Wrench Tether.  I value open access and innovation in tree climbing gear and I'm happy to make the AutoCAD file I used to design and cut these tethers freely available if people want to create their own or tinker with the design.  You can download the AutoCAD design file here.

If you want to order a ready to use tether from me then read on.

Cost:
I produce small numbers of hand assembled Zag-Wrench Tethers like the one shown above, which are available for $74 plus shipping.  USPS Priority Mail shipping within the USA is $7 and international shipping varies from $24 to $33 depending on the destination.

The tether can not currently be shipped to Germany due to a German customs guideline stating that any climbing gear that does not have a CE stamp can not be imported.  See here for more information.

There is a 2 month warranty on the Zag-Wrench Tether.  Details in the FAQs below.

Design Features:
The tether is made of 5 separate pieces of T6 6061 aluminum bolted together with stainless steel button top bolts and stainless steel nylon locking nuts.  The aluminum pieces are cut on a CNC water jet cutter by a veteran-owned and operated local machine shop in central NC.  I polish the pieces, assemble the main body of the tether, and construct the D shackle and clevis pin tending/attachment point by hand.


D Shackle and Tending Point. The 3/8" stainless steel wide D shackle doubles as the tending point when climbing the line.  The stock screw pin that comes with the shackle is discarded and the shackle is modified by filing out the threads so that an alternate stainless steel clevis pin can be substituted.  This is done so that the screw pin can not accidentally work its way out of the shackle with out the climber's knowledge.  The clevis pin is held in place by a stainless steel locking ring cotter pin.  The clevis pin, shackle, and cotter pin are attached to a flexible stainless steel 3/64" wire rope lanyard so that the individual pieces can not be lost even when the Zag-Wrench Tether is disassembled.

No-drop lanyard holds all parts of tending/attachment shackle to Zag-Wrench Tether
Protection for the ZigZag. Nylon washers are glued to the inner cheeks of the tether where it connects to the ZigZag to prevent scratching of the ZigZag.

Padded Wrench Bump Stop. To keep the Rope Wrench in the proper orientation and prevent it from collapsing on the Zig Zag, a small 3/16" Chicago bolt is inserted in one of the holes in the semicircle near the top of the tether.  Precisely placed latex bumpers surround the Bump Stop so that your Rope Wrench does not get scratched.  The holes for the Bump Stop allow you to use the setup on 11-13mm ropes.  (Note that Petzl states that the ZigZag should be used with 11.5-13mm ropes, but many have found that it works equally well on 11.0 mm ropes such as Yale Blaze as pictured above.)

Due to the small parts and critical nature of the Bump Stop, a spare Bump Stop is mailed with each Zag-Wrench Tether.


Ordering:
If you'd like to buy a tether please contact me at [email protected].  I will send you an invoice so you can pay with credit card.  Before I ship a tether I ask that the buyer sign a waiver stating that you understand the risks and experimental nature of the Zag-Wrench Tether.  (See text of waiver in English here o en Español aquí.)  Once your tether ships I will send the tracking number to you by email.  The cost is $74 plus shipping as described above.



FAQ:

Q. Is there a warranty on the Zag-Wrench Tether?
A. If within 2 months of delivery of your tether you are not satisfied for any reason you can send the unmodified tether in good condition back to me for a full refund of the purchase price not including shipping.  There is no other warranty or guarantee.

Q. How do I know which hole to put the Bump Stop in?
A. The Bump Stop for the wrench should go in the upper most hole that still allows smooth tending during ascent. The Zag Wrench Tether is designed to work with ropes from 11-13mm with the upper-most holes most likely to be best for 11mm ropes and the lower holes for larger diameter ropes.   It is the responsibility of the user to verify that the hole chosen allows the Wrench to engage immediately on sit back.  See the Intro Video at the top of this page for detailed instructions.

Q. Does Petzl state that the ZigZag can be used in an SRT setup?
A.  Petzl does not endorse pairing of the ZigZag and the Rope Wrench and they prohibit use of the ZigZag on a single line without additional friction.  Therefore the Zag-Wrench Tether should be considered an experimental device. Using the ZigZag in a way other than that described in the product information manual will void the ZigZag warranty.  As with any new climbing technique or tool, please practice low and slow until you are comfortable with the tether.  Please also regularly inspect the ZigZag for wear that could be accelerated by use in an SRT system.

In Section 4.2 of the ZigZag owner's manual (see image below or access the document at this link or this link) Petzl states that the ZigZag can be used in a "simple" or SRT setup as long as additional friction is placed on the line. The example they give is a Munter hitch below the line (see below).  A Rope Wrench above the ZigZag is another example of extra friction on the line, but it is not specifically endorsed by Petzl.

Q. What is the breaking strength of the ZigZag?
A. The ZigZag has been tested by Petzl and shown to withstand a force of at least 15 kN or 3375 pounds (15 kN is the European standard).  That means that the link side of the ZigZag can withstand at least 7.5 kN in the approved doubled rope setup.

Q. What percentage of a climber's weight does the Rope Wrench divert from the ZigZag?
A. According to the ZK2 Rope Wrench Owner's Manual the Rope Wrench "is a load-bearing device that may bear more than 50% of the climbers weight during the climb".  Independent analyses have shown that the Rope Wrench can take up to 2/3 of the climbers weight.

Q. Does using the ZigZag on a single line with the Rope Wrench result in an unfavorable orientation of the ZigZag?
A. The Zag-Wrench setup tilts the orientation of the ZigZag toward the lower rivet compared to the orientation during DRT usage.  For this reason users of the Zag-Wrench tether need to regularly inspect the ZigZag for wear of the swivel, rivets, links, and lower plastic housing.
ZigZag in SRT setup. From section 4.2 of the Petzl ZigZag Owner's Manual (click on image for higher resolution)
The Zag Wrench Tether is sold and warranted by Brandt Endeavors, LLC in Mebane, NC.  Brandt Endeavors, LLC is registered to do business under the names Piedmont Tree Climbing and Tree-minded Tree Care.