Sliding door lock, twin bolt

The factory latch on a sliding patio door is a hook that engages a single point and can usually be lifted clear by working the sash upward in its track. A twin-bolt lock sets two hardened pins through the sliding panel into the fixed frame, at the top and at the handle height, so the panel can neither slide nor lift.

Drills into the frame with a template supplied. Works alongside the security bar on plate 9 — the bar stops the slide, this stops the lift, and a patio door needs both.

Fitting and care. Drill into the fixed frame, not into the sliding panel’s glazing bead, and use the template supplied rather than eyeing it — a bolt that binds because it is a millimetre off will stop being used within a fortnight. Fit the upper bolt near the head of the panel where a lift attack applies leverage. Check the alignment again after the first hot spell, because aluminium frames move. Keep the bolt holes clear of debris and put a drop of dry lubricant on the pins once a year.