THE D SHAPED CARABINER IS LARGER and has a wider gate opening than the Oval. This shape is the “standard” carabiner. This will pair well with any decent device, and is most commonly used.
THE PEAR SHAPED CARABINER (aka the “Offset D”) will have an extra-large gate opening. You can use this carabiner to anchor several ropes or other gear together, which is very handy! These Pear shaped carabiners can sometimes be more difficult to operate, especially if you have smaller hands.
SCREW GATE OR “MANUAL LOCKING” CARABINERS will need to be manually twisted to open and shut the gate. Many people prefer Screw Gate carabiners because they like manually locking the carabiner themselves rather than relying on an automatic mechanism. Screw Gate carabiners are popular with recreational users and fire departments. In some countries they are also popular with rope access technicians.
AUTO-LOCKING OR “SELF-LOCKING” CARABINERS will automatically close when the gate is released. They are available in non-locking (open) double locking (twist-open), and triple locking (pull-twist-open). ISC even offers a quad-locking carabiner… but for 99% of applications that just excessive. Double locking carabiners are by far the most popular because they are easier to operate, especially when wearing gloves. Non-locking carabiners should only be used for non-critical applications. Auto-Locking carabiners are popular in industrial work such as tower climbing and rope access.
THERE ARE ALSO SOME SPECIALTY GATE OPENINGS. Petzl makes the Ball-Lock (which sounds really painful!). It has a small button that you push in to open the gate. Rock Exotica makes the Orca Lock which is half triple-lock and half non-lock. You can make the gate stick in the non-lock position so that it can be easily clipped onto things. Then once the gate opens and closes it automatically switches back to triple locking.
AND THEN THERE’S THE BLACK DIAMOND MAGNETRON (awesome name, right?). Its locking mechanism uses magnets. It’s the coolest carabiner you’ll ever hold. It’s not rated for industrial use unfortunately, but still worth checking out. You can find one at REI.
OF COURSE WITH ANY PIECE OF EQUIPMENT you want to make sure you are using your hardware properly. If used incorrectly you can reduce the overall strength of the carabiner, and even bend or break the hardware.
Your carabiner is much stronger on the major axis, which is where you will want any load hanging from. Whenever you have a load that isn’t on the major axis, that’s called cross-loading. Make sure to avoid cross-loading your carabiner by loading in the correct position, with the gate facing you to prevent your gate from opening.
Always make sure that your gate is fully closed before using it. Even Auto-Locking carabiners can “stick”, so double check before hanging on them.