Its curved arm hooks over a wedge fixed to the frame.

The handle is the lock rather than driving one.

There is no gearbox or rod involved.

The shape of the hook is what holds the sash closed.

It is the simplest window locking arrangement there is.

It is characteristic of older aluminium and timber windows.

The vertical offset between the fixing face and the arm that hooks the wedge.

It has to match the relationship between sash and frame on that window.

Step heights vary between windows and manufacturers.

The wrong step will not reach the wedge at all.

Or it will not pull the sash tight against its seal.

Measuring the existing handle before ordering is the reliable approach.

Emphatically - the arm curves one way and cannot be reversed.

The wrong hand points away from the wedge.

It then cannot engage at all.

This is the pattern where handing catches people out most often.

Handing conventions differ between manufacturers.

Checking their definition rather than assuming avoids a return.

Limited by design, and frequently supplemented on accessible windows.

A cockspur holds the sash but is straightforward to defeat.

Insurers commonly require a locking version with a key.

A separate window lock is sometimes required in addition.

Whether it is a requirement is a matter for the policy.

Where the window is an escape route, local regulation takes precedence.

The wedge has probably worn rather than the handle.

A worn wedge lets the sash move despite correct engagement.

Replacing the handle alone will not fix it.

Wedges are inexpensive and usually simple to replace.

Seal compression depends on both handle and wedge together.

Checking both before ordering avoids fixing only half the problem.

Usually at the pivot rather than anywhere visible.

External-facing hardware corrodes from the inside out.

Coastal and exposed locations accelerate it.

The handle becomes stiff and then seizes or snaps.

A handle that has become difficult to operate is usually corroding.

Replacing before it seizes is easier than dealing with a jammed window.

Locking cockspur handles are a direct upgrade where the geometry matches.

They retain the same hooking action with a key added.

Step height and handing still have to match.

Separate window locks are an alternative route.

Replacing the whole window is the larger option.

For insurance compliance the locking handle is usually the cheapest acceptable step.