What’s that bit for?

QWhat’s the use of the heel ledge on my winter walking boots? Nic Sparks, Nottingham

Trail says Some 4-season boots, B2- or B3-rated, may feature a protruding shelf or ledge on the heel. This ledge makes the boots crampon-compatible as it allows C2- and C3-rated crampons, with heel clip bindings, to be securely fitted to them. These types of crampons are generally easier, quicker and more versatile to fit than strap-on crampons, which is important in very cold conditions.