Karabiners

Karabiners, crabs, snap links or any other abbreviation that you use for karabiners are the links between practically everything that climbers and mountaineers use. They are arguably the most important invention in climbing history and I would imagine every climber in the UK has at least one.
 
Having said that there are lots of different types of karabiner in different materials designed for different things. In this guide I will attempt to highlight the different designs and what they are for.

Firstly the numbers stamped into the side of a karabiner are quite important and give the safe working forces of the karabiner. The double-headed arrow pointing along the back (longest side) of the karabiner is the tested minimum breaking force of the karabiner in that direction, along the major axis. It is rated in KN (Killer Newton's) and will normally be between 20 and 30.
The double-headed arrow pointing across the karabiner shows the minor axis strength. This is also rated in KN and will normally be between 8 and 12. This highlights how important it is to use the karabiner in the correct orientation, as it will be about twice as strong along the major axis.
The third number will have a diagram of a karabiner with its gate open. This is the strength of the karabiner along the major axis with the gate open. This will normally be about half the strength of the karabiner with the gate closed.
The other important numbers on the karabiner are the CE marks and the batch number. The CE mark shows that it conforms to European safety standards. The batch number allows you to trace the age of the product and will be used to recall any products if there are any problems identified.

 

Karabiners used to be made of steel, which is very strong but also very heavy. Modern karabiners are nearly all made of an Aluminium alloy that is still easily strong enough but is much lighter. Steel karabiners are still made and normally have a breaking force of about 45KN.

Gate Types:   

Screw gate
     The basic gate type for all belay and main anchor points. The locking gate stops the gate opening on impact or accidental opening. These gates can be simply screwed shut or there are quick lock versions available that spring closed.

Plain gate
     The basis of most racks. A simple sold gate karabiner used for racking, protection or extending gear.

Bent gate
     A solid gate karabiner like the plain gate above but with a bend in the gate. This stops the rope sitting against the gate and helps orientate the karabiner towards its strongest axis. Designed for the rope end of Quickdraws.

Wire gate
     Wire gates are replacing plain and bent gates for most uses that don't require a locking karabiner. Wire gates are lighter, simpler and wont freeze closed. The lower weight of the gate means that they suffer less from gate opening on impact.  

Shape:

Standard karabiners are D shape with a straight back and a curved front incorporating the gate. This is a strong shape because it puts the force along the straight back of the karabiner. The D shape is ideal for most normal applications.
The HMS karabiner was designed for using a Munter hitch to belay with. The pear shape of these karabiners gives a large area to belay on and hence these karabiners are designed for belaying on.
Oval karabiners are not used much any more because the design is not as strong as D a shape karabiner. They are however essential for use with some rope devices like pulley's and the mini traction. This is because the device needs to be positioned centrally on the karabiner to prevent a twisting sideways load. Aid climbers also favour oval karabiners partly because they are more comfortable to pull on.