Internal door hinges are single-axis butt hinges and spring hinges made for timber door leaves inside a building, carrying the full mass of the door on two or three fixing points. UAP supplies internal door hinges as seven separate product lines: ball bearing butt hinges, fixed pin butt hinges, loose pin butt hinges, loose pin hurl hinges, button tipped hinges, single action adjustable spring hinges and fire rated door hinges. Every line is morticed, so the leaf sits flush in a recess cut into the door edge and the frame instead of standing proud on the face.
Internal door butt hinges split into three constructions, and the split is a fitting decision rather than a quality ranking. A fixed pin butt hinge has a permanently riveted pin, so the two leaves never separate. A loose pin butt hinge uses a removable pin, letting the frame leaf and the door leaf be fitted independently. A ball bearing butt hinge runs on sealed bearing races and takes heavier leaves and higher traffic than either plain-pin type.
Loose pin construction earns its place on site through sequencing, not through convenience. A fitter hanging twelve doors in a new-build plot can screw every frame leaf into the linings, let the decorator finish the frames with the doors still stacked flat, then drop each leaf onto its pins in a single afternoon. The same job with fixed pin butt hinges forces one person to hold a 30 kg leaf square while a second drives screws. UAP lists loose pin butt hinges at 70 mm x 100 mm and 49 mm x 75 mm across zinc, electro brassed, chrome, white, black and matt steel.
The removable pin stops being an advantage the moment the door faces outward. UAP marks the ball bearing butt hinge range for internal use only, and that restriction has nothing to do with load capacity. Corrosion sets the boundary, not strength. Specifying an internal hinge on a back door because it feels more substantial than the external equivalent is a specification error that shows up as pin seizure within two winters.
Corner geometry has to match how the recess was cut, and most buying guides skip this entirely. Factory-prepped door leaves arrive with router-cut recesses that leave a rounded internal corner, so a radius corner hinge drops straight in. A hand-chiselled recess produces a sharp internal corner and takes a square corner hinge. Fitting a square hinge into a routed recess leaves four visible gaps at the corners; fitting a radius hinge into a chiselled recess leaves the leaf sitting on unremoved timber. UAP catalogues both geometries, including radius and square variants of the Certifire ball bearing hinge at 102 mm x 76 mm x 3 mm.
Internal door spring hinges close a door automatically without an overhead closer arm crossing the head of the frame. The spring sits inside the hinge barrel and is tension-adjustable, so the closing force can be set to the weight of the specific leaf. UAP rates the single action adjustable spring hinge at 100,000 cycles on its published tech sheet, dimensioned at 75 mm x 100 mm and supplied in pairs with fixing screws in electro brass, satin chrome and polished chrome.
Internal door spring hinges suit doors that must return to closed for reasons of privacy, draught control or containment, but where a visible closer body would be unacceptable. Utility rooms, plant cupboards, kitchen-to-hallway doors and doors on a domestic staircase all fit that description.
A spring hinge is not a substitute for a certified door closer on a fire door assembly, and treating it as one is the most common error in this part of the category. Fire resistance is a property of the whole assembly, tested together, and the closing device has to be part of that tested combination. A general-purpose spring hinge is not. Where a door must self-close and also hold a fire rating, the closing device belongs in the fire rated specification, and the hinges are then chosen to match it.
Substrate and finish are two separate decisions on interior door hinges, and retail listings collapse them into one. The substrate is the metal the hinge is made from: steel, stainless steel, or in the case of UAP fire rated door hinges, SS201 stainless. The finish is a plating layer applied over that substrate. Load capacity, cycle life and fire performance all come from the substrate. Appearance and wear resistance come from the finish.
Electro brassed does not mean brass. An electro brassed internal door hinge in the UAP range has a steel core carrying the load and a thin brass-toned plating carrying the look. This distinction matters when a specification calls for brass ironmongery on a fire door: a brass-plated steel hinge is acceptable because the steel core is what was tested, while a solid brass hinge is not, because brass softens at a lower temperature than the assembly needs to survive.
Finish choice on interior door hinges is otherwise driven by what the rest of the room already uses. UAP publishes ball bearing butt hinges in nine finishes including satin nickel, satin chrome, matt antique bronze, electro brassed and black nickel, so hinges align with handles and escutcheons already fitted.
Grade under BS EN 1935 is the number that tells you whether an internal door hinge can carry a given door, and it is the only figure on a hinge spec that is independently verified. The standard uses an eight-digit classification, and the final digit is the hinge grade, running from 1 to 14. UAP declares Grade 13 on its Certifire ball bearing fire door hinge, alongside CE marking and compliance with EN 1935:2002.
Grade ratings are tested with three hinges per leaf, and this is where specifications quietly break. A Grade 13 hinge does not carry a heavy door on its own, and it does not carry that door on two fixings either. Dropping from three hinges to two on a leaf specified against a grade rating voids the load figure that justified the choice.
Internal door hinge sets exist because hinges are manufactured, plated and packed in pairs while doors are frequently hung on three. UAP supplies the butt hinge and spring hinge lines in pairs complete with fixing screws. A door needing three hinges therefore consumes one and a half packs, and a plot of eight such doors consumes twelve pairs exactly. Buying to that arithmetic in advance prevents the mid-project shortfall that sends a fitter to a merchant for two loose hinges.
Batch consistency is the second and stronger argument for internal door hinge sets. Plated finishes vary between production runs, and the variation is small enough to pass inspection on a single hinge and obvious enough to see when two runs meet on the same door edge. A satin nickel hinge from one batch beside a satin nickel hinge from another can read as two different colours in raking light from a landing window. Ordering internal door hinge sets in one transaction, for the whole plot rather than door by door, keeps every leaf on one plating run.
Internal door hinge sets also solve the screw problem. UAP supplies matching fixing screws inside each pack, plated to the same finish as the hinge. Screws bought loose rarely match, and a mismatched screw head on a black hinge is visible from across a room.
Size and count follow door mass, not door height, and mass is the figure most buyers never check. UAP catalogues internal door butt hinges in two working sizes: roughly 75 mm and roughly 100 mm on the long edge, with the exact dimensions varying by line. The 75 mm sizes cover lightweight hollow-core leaves. The 100 mm sizes cover solid-core, engineered and fire rated leaves.
Three internal door butt hinges become mandatory once a leaf passes the point where two fixings leave the top hinge carrying the whole load in shear. Hollow-core doors in bedrooms and cupboards sit below that point. Solid-core and fire rated leaves sit well above it. A specification that saves the cost of one hinge per door and returns as a dropped leaf, a fouling latch and a re-cut frame twelve months later has saved nothing.
Hinge width also has to sit inside the door stile, and this trips up heavy-hinge upgrades. A 100 mm hinge on a leaf with a narrow stile overhangs the door edge and stops the door closing flush. Checking stile width before upsizing prevents a return.
Interior door hinges serve four buyer groups, and each one prioritises a different property. Homeowners replacing worn hardware want finish match and a straightforward fitting. Door fabricators want dimensional repeatability across a production run so that routed recesses accept every hinge in a batch. Developers and housing providers want certification documents that survive a building control inspection. Heritage and conservation specifiers want the smallest visible knuckle that still carries the leaf.
The best internal door hinges for any given opening follow from three questions answered in order: what does the leaf weigh, does the door need a fire rating, and does it need to close by itself. Weight sets the size and count. A fire rating sends the specification to the fire rated line with its FD30 and FD60 test evidence, EN 1935:2002 compliance and two-year UAP guarantee. Self-closing sends it to internal door spring hinges, unless a fire rating is also present, in which case a tested closer takes over. Finish is settled last, because no finish decision changes whether the door stays hung.
