UCF vs UCFC vs UCFL vs UCFA: The Four Flange Types Compared

The four flange shapes

Each code describes a different flange outline:

• UCF — square four-bolt flange. The most rigid of the four, with bolts at the corners of a square.
• UCFC — round four-bolt flange with a locating spigot on the back face, so the unit centres itself in a bored hole.
• UCFL — two-bolt oval flange. Compact, with two bolts on the long axis and a rounded outline.
• UCFA — two-bolt flange with slotted holes, letting the unit slide for position adjustment before the bolts are tightened.

The bolt pattern decides first

Count the holes on the plate you are mounting to. Four holes at the corners of a square take UCF; four holes on a bolt circle take UCFC; two holes take UCFL or UCFA.

Drilling a new pattern is possible but rarely worth it on a repair. Matching the existing holes is faster and keeps the original load path.

What the spigot does

Only UCFC carries a spigot — a raised ring on the back of the flange that fits a matching bore in the plate. The spigot takes the radial load in shear instead of relying on bolt friction, and it centres the shaft automatically.

That makes UCFC the choice where the shaft must be accurately positioned, such as the end of a conveyor roller or a machine where two flanges share one shaft. The plate needs a bored recess, so UCFC is a design decision rather than a field swap.

When slots earn their place

UCFA slots let the unit move a few millimetres before the bolts are tightened. That helps where belt tension or shaft alignment has to be set on site, and where the frame was not drilled to a precise pattern.

Slots are not a substitute for a take-up unit: they allow a one-time adjustment during assembly, not continuous travel under load.

How to choose

Work in this order:

• Match the bolt pattern on the existing plate.
• If the shaft must be precisely centred and the plate can be bored, prefer UCFC.
• If space is tight and only two bolts fit, choose UCFL.
• If you need adjustment during assembly, choose UCFA.
• Otherwise the square UCF is the most rigid and the easiest to source.