The phrase "a cluster of three" is correct and usable in written English.
It can be used to describe a group or collection of three items, entities, or elements that are closely related or positioned together.
Example: "In the garden, there was a cluster of three vibrant flowers blooming together."
Alternatives: "a group of three" or "a trio of three".
A cluster of three rockets will be used for the landspeed record attempt later on.
A cluster of three young men in jeans stood facing the scene with their backs to a wall.
It would be easy to fall into cliches: a male death figure picks a man out of a cluster of three couples and disappears with him into blackness.
Vatersay, which sleeps five, is one of a cluster of three cottages near Fort Augustus at the top of Loch Ness.
A cluster of three earthquakes measuring up to 6.0 struck two days before Christmas, causing fresh damage to buildings, including the cathedral, and closing the airport.
The image is of a woman's face in profile with a cluster of three light-filled circles at the top of her head.
Eli Manning dropped back to pass, while a cluster of three Giants receivers streaked downfield together like jets in formation -- it's called a bunch-three route.
Already, a new project at HMP Swaleside, Kent – one of a cluster of three jails on the Isle of Sheppey – aims to revolutionise prison education.
Next to Westerdok is a cluster of three more artificial islands whose distinct character derives from the fact that they were created in the 17th century.
The constant in each picture is a wedge of bare trees in a horizontal format; in the center is a cluster of three farm buildings, presented so that two sides of each building are visible.
During a recent break in "Unfabulous," a kind of musical "Wonder Years" aimed at 13-year-olds, a cluster of three consecutive commercials featured what might be thought of, by harried parents at least, as occupation forces.
