The magnets arc length is 45 degrees and they are generally used in motors, both for rotors and stators. If you purchase 4 off these magnets (ARC375S), with 4 off ARC375N, you will be able to create a complete 360 degree (8 pole) ring.
A pack of 1 - 37.5 O.R x 33.5 I.R x 25 wide x 4mm thick N42 Neodymium Arc Magnet (North). The NORTH pole is on the inner radius and the SOUTH is on the outer radius. These Magnets are plated with 3 layers of protective coatings - Nickel + Copper + Nickel (Ni-Cu-Ni).
Pack Size: 1
Shape: Arc
Magnetic Face: 37.5 O.R x 33.5 I.R x 25
Thickness: 4mm
Plating: Passivation

Material: NdFeB
Max Temp (degrees C): 80
Fixing: Araldite/Loctite
Each magnet can support a steel weight of up to kg vertically from the magnetic face when in flush contact with a mild steel surface of equal thickness to the magnet. Each magnet can also support up to 0kgs in a shear position before beginning to slide down a steel surface under the same conditions. These magnets are held in place by the Araldite/Loctite and have a maximum operating temperature of 80 degrees C.