Shapes
Carabiners have three main shapes where each shape is designed to suit a different purpose. The three main shapes are the Oval, D-Shaped and Pear. The Oval is often used for
Trad Gear; many people use an oval for racking their nuts as ovals allow the nuts to spin around the carabiners easily so you can select the right nut quickly. Ovals are also good for setting up anchors as they do not tend to shift when weighted. Ovals are generally considered the workhorse carabiner. D-Shaped carabiners are used on
quickdraws because the bottom of the D is smaller, which keeps the
sling from moving around. Pear shapes are generally found on locking carabiners since they have a large gate opening and allow for more to be hooked onto the carabiner.

Locking Carabiners
Locking carabiners are carabiners that include a mechanism that prohibits gates from opening with a single movement. These include screw/twist locks and
auto-locking carabiners. When
belaying always use a locking carabiner. Locking carabiners are also used to connect directly to an anchor and other life dependent purposes.

Screw-gate and Auto-LockingScrew-Gate
Screw-gate locking carabiners must be manually locked by screwing the locking device to the top of the gate. This blocks the gate from being opened by mistake. Some models will have red or orange coloring to indicate to the user when the gate is not shut; this can be a nice feature especially at busy
belay stations.
Auto-Locking
Auto-locking carabiners are spring loaded and therefore automatically lock themselves. The advantage of an
auto-locking carabiner is that you will not forget to lock your carabiner. One disadvantage is that many
auto-locking carabiners require two hands to disengage. Another is that auto-lockers can jam and not correctly close (therefore always inspect your
auto-locking carabiner when using it). They also have a tendency to freeze up quicker in winter, so for alpine and ice climbing you may want to use screw-gates
Non-Lock Carabiners
Non-Locking carabiners are used everywhere that lockers are not: this includes
quickdraws, racking gear, and
clipping gear. The gates can always be opened so it's important to make sure they will stay closed where you use them.
Gate ShapeGate shapes (bent or straight) come into play with
quickdraws. A bent gate will often be used for the
rope end of a
quickdraw to allow easier
clipping. This also makes them easier to
unclip, so make sure to never use a bent gate biner on the bolt end of a
quickdraw. On the bolt end of the
quickdraw a straight gate will be used. Straight gate biners have many more applications than bent gate biners and are usually cheaper.
Wiregate versus StandardWiregate carabiners may look weak, but they are generally as strong, if not stronger than standard carabiners. Wiregate carabiners are more expensive than standard gates on average. On a
quickdraw, wiregates are often used as a substitute for the bent gate carabiner (though they can be used for either the bent or straight). Wiregate carabiners are lighter than a straight gate carabiner and have become very popular in the last few years as they allow you to carry more before being loaded down.
Shutter Gate Effect
'Shutter gate effect' (also known as 'gate flutter') is a rare condition created when a carabiner is slammed against the rock. The mass of the gate creates a force which can open the gate. Therefore the strength of the carabiner reduces from the 'closed gate strength' to the 'open gate strength'. A wiregate's gate has less mass and therefore is less likely to open in cases of 'shutter gate effect'.
Strengths
Carabiners are listed with three unique strengths measured in kilonewtons (kN). These are closed gate (CG), open gate (OG), and minor axis (MA). Closed gate strength is the most important and refers to the strength of the biner when the gate is closed and the forces are created at the bottom and the top of the biner (99.9% of the time). Open gate strength is the reduced strength of the carabiner when the forces created on it are the same as the closed gate, but the gate is open (due to the shutter gate effect or the biner pressed against the rock). Minor axis strength is when the biner has rotated and the forces are pressed against the gate and the spine of the carabiner.
