Carabiners (often shortened to 'crab' or 'biner') are the mainstay of the climbing system. They're used to attach the rope to pieces of equipment, or to join two or more pieces of equipment together. Carabiners are generally made of aluminium. Shapes vary, but it's always some kind of elongated triangle or oval, with an opening gate on one side to allow you to easily clip and unclip stuff. There are two main types: snapgates (non-lockers) and screwgates (lockers).
Snapgates are the simplest carabiners. They're used for clipping the rope to gear, but not for anything really important such as belaying or anchors. The gate can be made out of solid metal or a loop of wire: both work in the same way. Snapgates cannot be locked. Instead, a spring system snaps the gate shut.
Screwgate carabiners are used when you need to be 100% sure that the gate won't pop open. They're slower to use than snapgates, but safer. The gate features a rotating tube which spirals around a screw thread. The gate is locked when the tube is positioned over the carabiner’s nose. To unlock it, simply unfasten the screw. Don't be tempted to tighten the screw too much – it’ll be hard to unfasten.
You may also come across autolocking carabiners. The locking tube on these isn't threaded, but instead springs into place and needs twisting in a certain way to unlock. They're just as safe as screwgates, but can be fiddly to use at first.
How Strong are Carabiners?
Climbing carabiners are always rated to at least 20kN (kiloNewtons). You don't need to understand the numbers, but that's REALLY strong. Strong enough to hold an elephant.
They are weaker if you 'cross load' them (load them sideways) or load them with the gate open (another reason to use screwgates for important stuff).
The kN rating will always be written on the side of the carabiner; this is how you know your carabiner is safe for climbing and not just for your key chain.
How Many Carabiners Do I Need To Start Climbing?
Here's the good news: probably just one! When you're starting out at the climbing wall, you'll just need one screwgate carabiner for your belay device (see later).
If you want to climb outside, you can build up a 'climbing rack' over time that will include a lot of carabiners. There's no rush though; learn the basics first.