NRP Hinges: The Cheap Upgrade That Stops a Door Being Lifted Off
, by United Doors and Locks, 4 min reading time
On an outswing door the hinge pins face the street, and a door can be lifted out with the lock still thrown. Non-removable pin hinges stop it for a few dollars.
There is a category of security failure that defeats the lock entirely by ignoring it. On an outswing exterior door, the hinge barrels face the street. Tap the pins out from underneath, and the door lifts away from the frame with the deadbolt still thrown. It takes a screwdriver and about a minute.
The fix costs a few dollars per hinge.
What NRP means
NRP stands for non-removable pin. The hinge carries a small set screw, threaded through the barrel, which seats into a groove or hole in the pin.
The detail that makes it work: the set screw is positioned so that it is concealed by the frame when the door is closed. With the door shut, there is no access to it. To reach the screw you have to open the door — and if you could open the door, you would not be attacking the hinges.
Which doors need it
Any door where the hinge barrel is on the less secure side. In practice:
- Outswing exterior doors. The main case. Rear service doors, fire exits, mechanical yard access, loading doors.
- Outswing doors to secured interior rooms — IT closets, cash rooms, drug storage, evidence rooms — where the corridor side is not controlled.
- Any door whose hinges you can see from the public side. This is the test. Stand where an intruder would stand. If you can see the knuckles, specify NRP.
Inswing doors do not need it, because the barrels are already on the secure side. Specifying NRP on every hinge in a building wastes money on the majority of openings.
Note that outswing is extremely common on exterior commercial doors, because codes require egress doors serving certain occupant loads to swing in the direction of travel. Fire exits are almost always outswing. So are most rear doors on commercial premises — which is exactly where break-ins happen.
What to order
NRP is an option on the hinge, not a separate part, so it is ordered as part of the hinge specification. The BB5 NRP 4.5 by 4.5 inch ball bearing hinge is the standard commercial specification. For doors over about 200 pounds, or wider than 36 inches, or in high-frequency service, the heavy weight BB5-HW NRP carries thicker leaves and a larger pin.
The H4545 Series ball bearing hinge and the H4545 plain bearing hinge are both available in NRP variants, so on a mixed schedule you can keep one hinge family and switch the option per opening.
Two points worth pairing with it. First, an exterior door should be on ball bearing hinges anyway, because it has a closer. Second, if the exterior environment is wet or coastal, specify stainless steel — US32D (630) rather than US26D — since a plated hinge that corrodes at the barrel will seize long before the pin becomes anybody's concern.
Security studs: the same problem, a different answer
Some hinges use interlocking security studs instead of, or as well as, an NRP screw. A stud on one leaf engages a hole in the other when the door is closed, so the two leaves are mechanically locked together regardless of the pin.
Studs resist a spread attack — prising the door away from the frame — as well as pin removal. NRP addresses pin removal specifically. Where the threat model is serious, use hinges that offer both. For the ordinary case of a rear exit door, NRP alone is a large improvement over nothing.
Retrofitting an existing door
If the door is already hung on standard hinges, replacing them with NRP hinges of the same size is a like-for-like swap into the existing mortises, one hinge at a time, with the door supported. There is no new prep and it does not affect the lock or the closer.
Do not attempt to add a set screw to an existing hinge by drilling the barrel. The barrel wall is thin, the screw will not hold, and you will have weakened a load-bearing part.
Fire-rated doors
NRP hinges are used on rated assemblies routinely, but the hinge still has to be listed for the door. Use steel ball bearing hinges of the type the listing calls for and confirm the NRP variant is covered. Substituting a hinge on a labelled assembly, even for a stronger one, can void the label.
The short version
Walk the outside of the building. Every door where you can see hinge knuckles is a door that should be on NRP hinges. It is the cheapest meaningful security upgrade on a commercial building, and it is routinely missed because the hardware schedule was written from a plan rather than from the street.
Send us the exterior openings and we will mark which ones need it.