Crampons attach to your boots in a number of ways. It is important that your boots and crampons are suitable for one another and – as a rule – your crampons should be no stiffer than your boots. A rigid crampon with a flexible boot is liable to falling off, causing ankle injuries, and suffering metal fatigue or breaking.
Crampons can be categorised into 3 types, Flexible (C1), Semi-Rigid (C2), and Rigid (C3)(see Crampon Types). Boots can also be broadly categorised into 4 types as per the table below.
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This rating system refers primarily to the stiffness of the boot, with category B0 not being suitable for crampons. The stiffness of a particular model of boot will obviously vary depending on the size of the boot. The largest fitting will be more flexible than the smallest, meaning that people with big feet may need to select a stiffer boot than those with smaller feet.
Now that you know which crampons and boots are compatible with one another, you should consider crampon attachment or the binding system. The binding system is the means by which your crampons attach to your boots. It is important that your boots are designed to accommodate the binding system of your crampons and that they attach securely. A poorly fitted crampon can cause equipment damage or, worse yet, injury on the mountain.
There are three main types of crampon bindings: Strap-On, Step-In, and Hybrid.

Strap-On
As the name suggests, strap-on crampons feature nylon webbing that straps the crampon securely to the boot. If the centre bar is compatible with the flexibility of the boot, strap-on crampons will fit most boot types. Strap-on crampons take a little longer to attach and there is always a degree of play between crampon and boot. However, they offer a flexible solution and are suitable for snow walking and moderate ice climbs.
Step-In
Step-in crampons will only fit boots that feature heel and toe welts designed for step-in crampons. A wire bail secures the toe of the crampon and a heel cable with a tension lever clamps the crampon securely in place. Step-in bindings attach securely with little or no play and can be removed easily, even with thick gloves on. Step-in bindings usually feature an ankle strap and an adjustable front bail.
Hybrid
Hybrid or semi-step-in bindings feature – as the name suggests – elements of the other binding systems. There is a toe strap at the front of the crampon and a heel lever at the back. Hybrid bindings require a stiff sole and a heel grove to hold the crampon in place. However, they are more flexible and forgiving than a full step-in binding meaning that they do not have to fit perfectly into the heel welt. Hybrid crampons are easy to attach and remove in difficult conditions with gloves on.