The Mad Rock Gemini is a locking carabiner designed specifically for belaying that actually has two gates. Not only that, but it also has two separate chambers and openings, joined in the middle, making it one of the most unique, and bizarre, locking carabiner designs that we have tested. The purpose behind this design is to prevent the locker, or belay device, from rotating when belaying, and thereby avoiding cross-loading. It does this well, but at times comes across as perhaps a bit too complicated to achieve this purpose. While there is only one screw down lock, the hinges of the two gates overlap so if one gate is locked, the other one is also pinned closed. The two gates can also open at the same time, but the very small gate openings limit it to belay use. While it may look weird, the Gemini is an affordable and effective belay locker.
Mad Rock Gemini Review
Cons: Very small gate openings, opening top gate causes other to automatically open, not super versatile
Manufacturer: Mad Rock
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Our Analysis and Test Results
The Mad Rock Gemini is designed to prevent cross-loading while belaying, and for this purpose we found it to be quite effective. It has two gates that are linked together at the hinges, meaning that both gates are locked with a single screw-lock device. One gate is meant to be attached to the belay loop, and the other is meant to be attached to the belay device. Unfortunately, these overlapping hinges also mean that if you want to open the belay loop gate, the belay device gate opens automatically. This is not awesome if you are taking the locker off of a gear loop on your harness, as it is easy to accidentally drop the belay device off the lower nose, which is shallow. Because it is pretty much two tiny carabiners fused into one, the same problems we have with small carabiners also manifest — namely that they are harder to manipulate due to small gate openings. Despite our complaints we found this carabiner relatively easy to use, although if you are looking to buy the easiest and most versatile belay carabiner, we recommend the DMM Rhino.
We found that this carabiner generally does not perform as well as simpler, more standard pear or HMS shaped lockers, which we prefer for their ease of use as well as simplicity. While this locker works fine for use with a GriGri or other active assisted braking device, the small openings and upper basket make it a bit harder to use with an ATC, and not exactly ideal for rappelling with two ropes. The fact that both gates must open together means there is a greater risk of dropping a belay device off the top basket when removing the lower gate from your belay loop or a gear loop. Additionally, since the lower gate is pinned by the upper gate, to open it requires overcoming dual spring loaded gates, which is harder than simply opening a single gate, and oddly enough led to the gate closing with such force that more than once it pinched our skin. The small gate openings and small baskets mean it isn't super versatile for building anchors. While it isn't as hard to use as we are making it sound, it also isn't as simple as a regular old locker.
Ease of Unlocking and Locking
Since the two gates are pinned at the hinge, if you lock the top gate, then both gates will automatically be locked. There is no way to lock the lower gate by itself. To lock the gates a simple screw lock mechanism is involved. This screw locking mechanism is small, and only has added texture at the top and bottom, with slippery un-textured metal in the middle, making it not the absolute easiest to grip compared to the competition. We measured seven half rotations, or 3.5 full rotations, to go from fully locked to fully unlocked, which is also not the least that we tested.
Compactness and Weight
We measured the weight of the Gemini to be 72g on our independent scale, which actually makes it one of the lighter belay specific carabiners you can buy, but not by any means as light as a standard HMS or pear shaped locker such as the Petzl Attache. However, we bumped its score for this metric down a tad because of how large it is. It is taller than all of the others that we tested, so we can't consider it to be especially compact.
The Gemini features a single screw gate to lock it, which we find to be among the least secure. This isn't to suggest that they cannot be trusted, simply that screw gates have the notable flaw of needing to be remembered to be locked, rather than simply locking themselves. The screw gate on this locker has a red stripe that wraps around the gate to serve as a visual indicator: when it is fully locked, the stripe will not be visible. If you see red, then it isn't locked.
We can't decide whether having two gates makes it less secure or not. If you forget to lock it, then there are two potential gates that could conceivably open, instead of just one, but we can't really imagine scenarios where this might happen.
We measured the gate clearance for this locker at 1.6cm, which is among the lowest scores for this category. Both the top and bottom gates open the same distance, although if you open the bottom gate as far as you can, it automatically opens the top gate to a distance of only 1.2cm, which is the "gate clearance" number listed on Mad Rock's website. From a functional standpoint, larger openings greatly ease general use, and the very small openings on both ends of this carabiner are certainly a draw back, making us less likely to want to use it for anything besides belaying.
The Gemini is nowhere near as expensive as some of the higher priced belay-specific carabiners, but still costs slightly more than a Petzl Attache, or even our favorite belay carabiner, the DMM Rhino. While the price isn't out of line with performance, we would prefer to spend the same amount of money on a better product.
The Mad Rock Gemini is one of the most unique locking carabiners we have ever used, with two separate "chambers" accessed by two different gates, which both manage to lock with one single screw lock mechanism. While it works decently for belaying, it isn't super versatile for other applications. While we don't think it's a bad product, we would sooner recommend others for the purpose of preventing cross-loading.
— Andy Wellman