This is a 150mm Outside Diameter x 80mm Inside Diameter x 10mm Thick Neodymium Grade N52 Ring Magnet. NiCuNi Coating. Axially magnetized.

Converting those dimensions to imperial units, that is 5.905"OD x 3.149"ID x .393" Thick

Ring magnets have multiple applications; speakers, helicon plasma sources, fishing for metal at the bottom of a lake or river, energy generation, etc  

This is a very powerful magnet and can hurt you if you are not careful, read the warnings below.

WARNING:
This magnet is not intended for use with or as a magnet set. A magnet set is defined as any aggregation of separable magnetic objects that is a consumer product intended, marketed or commonly used as a manipulative or construction item for entertainment, such as puzzle working, sculpture building, mental stimulation, or stress relief.
Fingers could be severely pinched between two or more magnets.


KEEP OUT OF REACH OF ALL CHILDREN.
 THIS IS NOT A TOY.


DO NOT ingest or inhale.
DO NOT place in nose, mouth or any other part of the body.
Swallowed magnets can stick to intestines causing serious injury (NECROSIS) or even DEATH.
Seek immediate medical attention if any magnet(s) are swallowed or inhaled.
Neodymium Magnets are BRITTLE.
They can SHATTER, CRACK, PEEL or SPLINTER if allowed to snap together or slam into a metal object.
Broken magnets can be Extremely SHARP.
MAGNETIC MEDIA AND ELECTRONIC EQUIPMENT HAZARD.
KEEP AWAY from PACEMAKERS AND INTERNAL MEDICAL DEVICES.
Magnetized materials are REGULATED FOR AIR TRANSPORT and are considered a HAZARDOUS MATERIAL.
Neodymium magnets will lose their magnetic properties if heated above 175°F (80° C).
Do Not cut or drill Neodymium Magnets, there is a both a fire and fracture hazard and the dust is toxic.