How Many Ball Bearings Does a Door Hinge Need? 2BB, 4BB and 6BB Compared

Updated 2026-11-05 · RAYEN 雷茵

What does the BB number mean?

BB stands for ball bearing, and the number in front counts them. It sits at the end of the hinge code, so 4x3x3.0-4BB has four. In this range you will find 0BB, 1BB, 2BB, 4BB and 6BB.

DD is different. 4x3x3.0-2DD carries two copper gaskets and no ball bearings. Do not read it as a 2BB.

What do the bearings do?

A door hangs on its hinges, and the knuckles press on each other at every joint. A bearing sits in the joint, so the knuckles roll on it and do not rub metal on metal. The hinge turns more easily, and the joint wears more slowly.

Where do the bearings sit?

You cannot count bearings by counting knuckles. Compare two drawings of the same hinge size.

• 4x3x3.0-2BB US has five knuckles and four joints. Bearing rings sit at the two outer joints.
• 4x3x3.0-4BB US has five knuckles and four joints. A bearing ring sits at each one.
• 8x4x3.5-6BB has six bearing rings along its 203.2mm height.
• 4x3x2.5-1BB has two knuckles and one joint, so one bearing.

From a metre away, a 2BB and a 4BB can look alike. Check the code on the box and the rings on the barrel.

What changes between 2BB and 4BB on the same hinge?

Only the bearing count. Two pairs show this cleanly.

• 4x3x3.0-2BB US and 4x3x3.0-4BB US are both 101.6 × 76.2mm, 3mm, Ø14.2mm.
• 4x4x3.0-2BB US and 4x4x3.0-4BB US are both 101.6 × 101.6mm, 3mm, Ø14.2mm.

So you can move from 2BB to 4BB on these pairs with no change to the leaf size. Compare the drawings for the screw holes before you commit a door.

How many should you choose?

We print no load figure for these hinges, so treat the following as a starting point and not a rating.

• 0BB or 1BB: small or light doors, or where the hinge shape matters more than the bearing. 110x55x2.5-1BB and 100x89x3.0-1BB are shaped hinges with one bearing.
• 2BB: light room doors. The offset and centre pivot hinges, such as 4x3x2.5-2BB Centre Pivot, are all 2BB.
• 4BB: the default for heavier doors, busy doors, and doors with a closer pushing on them.
• 6BB: 8x4x3.5-6BB is the only one, at 203.2 × 101.6mm and 3.5mm thick.

Leaf thickness and knuckle diameter matter as much as the bearing count. 4x3x2.5-4BB has four bearings on a 2.5mm leaf with a Ø12.2mm knuckle. 4.5x4.5x3.5-2BB US has two bearings on a 3.5mm leaf with a Ø15.2mm knuckle. Neither wins by the number alone.

What should you measure?

• Door weight in kg.
• Door height and width.
• How often it opens: a bedroom or a hotel corridor.
• Whether a closer or a spring pulls on it.
• The leaf size you can fit, from your door and frame.

Hinges by bearing count

The chart starts at zero bearings and ends at six. The copper gasket models appear among the 2BB hinges, so watch the wording in the first column.

Brass hinges: 4BB or 2DD?

Brass comes with ball bearings or copper gaskets, and the two are not swaps. 4x3x3.0-2DD is 101.6 × 76.2mm with a Ø14mm knuckle. 4x3x3.0-4BB in brass is 100 × 75mm with a Ø12mm knuckle. If you change between them, you change the routing too. The size chart has every pair.

A worked example

A hotel orders doors with closers on every room. The leaf is 4 inch by 3 inch. Choose 4x3x3.0-4BB US rather than the 2BB twin, because the closer works the joint on every cycle and the leaf size stays the same. Send us the door weight and height, and we confirm the hinge and how many to fit on each door.

What should you write on the order?

• Full code with the bearing count, such as 4x3x3.0-4BB US US standard.
• Material. For stainless, state 304 or 201.
• Leaf size in mm from the chart.
• Finish and quantity.
• Door weight and height, so we can check the choice.

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