The Triple Attachment Pulley proved a success in tree climbing competitions and industry presentations after its release in 2006. Mark Bridge and Chris Cowell of Treemagineers quickly became aware of the need to develop a high-performance connector to compliment the evolution of the Triple Attachment Pulley and improve safety and efficiency in professional tree care.

“When we were carrying out tree related jobs, we realised that we weren’t differentiating between connectors very well,” says Mark. “We needed a new carabiner that was as wide as possible and flat at the top.” 

Before the invention of the Triple Attachment Pulley, HMS carabiners were widely used in both climbing and working at height. It was the arrival of the Triple Attachment Pulley that encouraged a widespread change in the requirements for connector carabiners. 

Employing the new Triple Attachment Pulley in tree climbing systems meant that it was now possible to connect multiple carabiners to a central point without overloading the pulley. The friction hitch cordage could be attached to the lower connector which in turn linked to the attachment point of the harness, and the spliced termination of the climbing line could be attached to the upper connector. 

“This encouraged us to switch to oval shaped connectors,” says Mark. “In this configuration the connectors are now not only well positioned to improve the efficiency of the system, but also they are being used in the way they were designed and tested.”

Oval carabiner family

When Mark and Chris discussed design specifications with the team at DMM, they set out to manufacture a connector which was as strong, resilient to wear as possible and versatile.

Mark points out that true oval carabiners are not easy to make. “This is due to their equal width top and bottom and the distance between the opening and spine. Other carabiner shapes such as modified D-forms are biased towards the spine, i.e., their strongest side—or have a wide and narrow width at the top and bottom respectively, as is the case with an HMS shaped connector. A true oval is symmetrical in the major as well as the minor axis. The ability to make this shape strong requires design and manufacturing savvy.”

“Due to manufacturing limitations at the time, we thought that oval shaped connectors were not really an option. However, when we started thinking about the core requirements of connector carabiners, all of a sudden the oval became a really interesting option. With the arrival of the Triple Attachment Pulley we freed ourselves from the constraint of having to fit all the gear into the top of the carabiner and could now focus on the core function of the connector.”

Hot forged carabiner barHot forged carabiner pressed
Hot forging aluminium Ultra O

An oval carabiner is a product which is difficult to design and manufacture to a high standard. “We were lucky to work with DMM who could deliver on both fronts,” says Mark.

From an evolutionary point of view, the Triple Attachment Pulley paved the way for oval carabiners becoming ubiquitous in tree climbing systems. According to Mark, “if you go back 15 years that wouldn’t have been the case and we would have seen more modified HMS shapes and other whacky carabiners being used as connectors.” Today, ovals are one of the more wide-spread shapes used in tree climbing.

They also found favour among rope access technicians looking for a lighter-weight option compared to the industry standard heavy steel ovals.  An oval gives stable loading characteristics when repositioning, as attachments can ‘self-centre’ with minimal disconcerting movement from the connector.

“When the Ultra O was released there weren’t many interesting oval shaped carabiners on the market. Today, it is my go-to carabiner,” says Mark. “If the Triple Attachment Pulley is the Thomas the Tank Engine of tree climbing equipment, then the Ultra O is the humble tractor. Incredibly versatile, it is a product that does everything incredibly well.”


UltraO in actionUltraO DurolockUltraO captive bar

DMM now manufacture Kwiklock, Locksafe and Durolock versions of the Ultra O, ideal for assisted braking devices, pulleys, swivels and shackles. As evolutions of the classic carabiner, the oval connector range now also offers the compact PerfectO and the larger AmericanO for when more volume is required.

The AmericanO is DMM's first ANSI (American National Standards Institute) compliant true oval connector—ideal for those working at height and needing an oval that can be used within the ANSI proof loading constraints.

The non-locking PerfectO provides colour coded options as a racking carabiner for trad climbers using Wallnuts, Alloy Offsets etc.

While the oval shape provides stable loading characteristics for industry practice, the same silhouette can be seen in miniature with the popular XSRE and XSRE Lock (non-PPE) accessory connectors.

As Mark points out, “we have a whole family of oval shaped carabiners now, which I believe is indicative of how versatile the shape is. The oval accommodates basic beginner systems as well as advanced techniques, offering a broad platform that will accommodate all sorts of systems when used in the field. The reversibility and the option to rig ovals back-to-back is also certainly a reason for its popularity.” 

With the relationship between DMM and Treemagineers continuing to grow, the development of the oval carabiner is far from over. “If I had to put my finger on something which stands out in our collaborations with DMM,” says Mark “it’s that the products are so well thought out and designed.” Working together to design new gear and make improvements to classic pieces of equipment, DMM and Treemagineers have developed a range of connectors and an industry standard oval carabiner which is an integral element in the wider evolution of tree care kit.