Step by Step Guide to identifying an Espagnolette (Espag) Window Lock

An espagnolette (espag) uPVC window lock is the gearing part inside a window that a spindle drive uPVC window handle operates and locks the sash to the frame, it seals from drafts and also secures the window shut.  The picture below shows one of many different types.  You measure from the middle of the spindle hole to the top of the face rail, this will give you your backset.

Dimension A– Middle of Spindle Hole
Dimension B– Backset – Measurement from middle of spindle to the face of the rail, usually 20mm, 22mm, or 25mm.

Know which lock you need? 

Espagnolette window locks have different backset measurements. It is important that the backset of the replacement is the same as the backset of the original otherwise modification of the window frame may be required. There are three holes in the side of every gearbox, the centre one being the spindle hole and the other two screw holes for the handle. The distance between these three holes is universally the same at 43mm.

The difference between offset and inline espag uPVC window locks

The inline mechanism has the gearbox in the middle of the rail and as above the offset has the gearbox off to one side of the rail.

There are many different makes of window mechanism rail locks and they can be changed for other makes as long as the basics of the cams (roller or mushroom cams) are the same backset, rail length, rail width, cam height, and still inline or offset. If a different make is used but they are otherwise very similar then it is likely that the keeps will need to be re-positioned due to the cams being in a different position on the rail. On occasions, the hole for the gearbox in the window frame may need to be enlarged when using a different brand but it is rare.

Mechanisms also have another difference between the offset and inline, the inline has a flat rail and the offset has a u shape rail.

Most modern mechanisms have mushroom cams, they are called this for the shape of the came, (roller wheels going up and down when the handle is turned) These can be adjusted using an Allen key or sometimes a flat-headed screwdriver to increase compression on a slack window (symptom: handle goes into closed position too easily) or decrease window compression on an over tighten window (symptom: the handle has to be forced into closed position)