Window Hardware - Double Hung

Double hung window hardware: locking two sashes at the meeting rail

Double hung window hardware in this group locks the upper and lower sash together where they overlap, the horizontal meeting rail partway up the window. Unlike a casement window's crank-driven swing, a double hung window slides straight up and down, and its lock only needs to hold the two sashes against each other rather than drive any motion itself.

How the meeting rail lock works

Turning the cam on a double hung sash lock, like the DHSL100 or DHSL200, draws the lower sash's top rail up against the upper sash's bottom rail, closing the small gap between them and pulling both tight against their frame. That tension is what stops the window from being pried open from outside and, as a secondary effect, cuts down on the draft that gap would otherwise let through.

WD and SL model differences

The WD130 and WD10 differ mainly in cam length and backplate size rather than how they operate, while the SL100 uses a slightly different housing shape for the same basic function. None of these interchange freely with hardware from a different window manufacturer, since the meeting rail's exact profile varies enough between brands that a cam sized for one won't always seat flush on another.

When to replace rather than repair

A double hung window that won't stay locked, or rattles at the meeting rail even when the lock is engaged, usually needs a new lock rather than an adjustment, since the cam mechanism wears with each turn over years of seasonal use. Confirm the existing model number where possible; matching it exactly avoids guessing at cam length or backplate spacing on a window that's otherwise still in good shape.

One lock, two sashes to check

Because a double hung lock engages both the upper and lower sash at once, a window that still rattles after a new lock is installed sometimes has the problem elsewhere, a warped sash or a worn track rather than the hardware itself. Test the lock with both sashes fully seated before assuming a second replacement is needed.