An anti-burglar bolt — often called a *dog bolt* — is a vertical or horizontal steel stud or bar fitted on the hinge or lock side of a window, shutter or door, designed to stop the leaf being pried out of its frame even after the hinges have been cut. It is a traditional form of intruder protection, frequently seen in original condition on older buildings.
How it works
On a typical window or shutter, the hinge side is the weak point: cut the pins or wrench off the hinges and the whole leaf comes free, regardless of how good the lock is. A dog bolt prevents that:
- On the hinge side — a fixed stud on the leaf engages a recess in the frame. Even without hinges, the leaf remains locked into the frame
- On the lock side — a counter-stud stops the leaf being levered sideways
- At the top — on tall shutters, a stud prevents the leaf being pushed upward and out
Application
Dog bolts have been used on:
- Exterior shutters on heritage buildings — fitted on the back of the shutter
- Old houses with casement windows — easily forced open without one
- Warehouse and storeroom doors — typically in a heavy version
- Cellar doors and coach gates — often combined with a slide bolt system
Modern equivalents
In current door and window hardware, the dog bolt principle survives as:
- Anti-lift hinge pins — fixed pins on the hinge side of an external door that engage holes in the frame as the door closes
- Security hinges — with a built-in stud or fin that interlocks with the frame
- Multi-point locking — three or five points engaging the frame simultaneously
Restoration considerations
In heritage buildings, original dog bolts should be retained where possible. When replacing:
- use wrought iron or stainless steel in the original dimensions
- fasten with hand-forged clinch nails or dowels
- install after painting, so the bolt does not rust into the wood
Related terms
- Burglar bar
- Anti-burglar hardware
- Hinge
- Multi-point lock
- Shutter
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