Cal-Royal BB31 Full Mortise, Standard Weight, Two Ball Bearing Hinge, 4 1/2" x 4 1/2" - Template - Box Of 3

The Cal-Royal BB31 is a full mortise, standard weight, two ball bearing door hinge in a 4-1/2" x 4-1/2" template configuration, sold as a box of 3 hinges. It's the specification butt hinge for standard weight commercial interior doors receiving average frequency service in offices, schools, hotels, multi-family residential buildings, and institutional facilities where the door schedule calls for a two-bearing full mortise hinge in the 4-1/2" leaf size.

What Full Mortise Means on the BB31

Full mortise means both leaves are routed into the door and frame, not applied to the surface. One leaf is mortised into the door edge; the other is mortised into the door frame jamb. The result is a hinge that sits completely flush with both surfaces, with no projection beyond the face of the door or the jamb face. Full mortise is the correct installation type for hollow metal doors with hollow metal frames, wood doors with wood frames, and hollow metal doors with wood frames. Both leaves sit completely within the material on each side of the opening.

Two Ball Bearings: What They Do and Why They Matter

The BB31 carries two stainless steel ball bearings positioned between the hinge knuckles. Ball bearings reduce friction between the knuckles during every open and close cycle, which distributes wear more evenly and extends the operational life of the hinge under average frequency door use. On a standard weight interior door that opens and closes dozens of times daily, the ball bearing design prevents the binding, squeaking, and knuckle wear that plain bearing hinges develop over time. The BB31 is specifically rated for standard weight doors receiving average frequency service, which covers the majority of commercial interior door applications in the 4-1/2" leaf size range.

Specifications

• Size: 4-1/2" x 4-1/2"

• Type: Full mortise

• Weight class: Standard weight

• Bearings: 2 ball bearings

• Gauge: .134 steel

• Screw hole pattern: ANSI template (A156.7)

• Tip style: Flat button tip standard; hospital tips available

• Pin: Standard removable; NRP (Non-Removable Pin) available by adding NRP to model number

• Sold as: Box of 3 hinges

ANSI and BHMA Compliance

Cal-Royal BB31 hinges comply with ANSI A156.1 (Butts and Hinges), ANSI A156.7 (Template Hinge Dimensions), ANSI A156.17 (Self Closing Hinges and Pivots), and ANSI A156.18 (Materials and Finishes). BHMA certified. The ANSI A156.7 template compliance means the screw hole pattern matches the industry-standard template, making the BB31 a direct interchange for any ANSI template full mortise hinge from other manufacturers including Hager BB1279, McKinney TA2314, and Stanley FBB179 in the same 4-1/2" x 4-1/2" standard weight class.

Material and Finish Options

The base BB31 model is steel, available in multiple architectural finishes. For stainless steel base metal, order BB31 US32D. For solid brass base metal, use the SB prefix (SBBB31). Hinges are stamped with the CRP logo as standard; to order without the logo, add the UN prefix (UNBB31). All plated finishes carry a clear baked topcoat. Available finishes include US26D Satin Chrome, US32D Satin Stainless Steel, USP Primed for Paint, US3 Bright Brass, US4 Satin Brass, US10B Oil Rubbed Bronze, and US26 Bright Chrome among others. Cal-Royal offers a lifetime warranty on all commercial grade hinges.

.