How strong are the magnets in these bracelets?

Not sure...did not wear the bracelet long.

What size is the ring?

They are about 3 inches in diameter, but can fit almost any wrist because they are open and can be adjusted to take the contour of your wrist. They fit both me and my husband.

Do these bracelets relieve arthritis pain from all over the body or only the hand?

My son 51 yrs old has Rheumatoid Arthritis, my sister 65 years old had her fingers starting to curl one on top of the other, finally my Step Father had a job that almost crippled his hands. I first bought them for my son and they worked great. I told my sister and bought her some, to this day all her fingers are straightened out and no pain. Bought them again for Step Father he is 80 years old and now has no pain. I am really impressed with them, I didn't believe until I saw the results, especially with my sisters fingers.

How wide is the bracelet and is it one size fits all/fits small wrists?

Dear Customer, Thank you for asking this question, It's my pleasure to answer you. The Hammered solid bracelet is 0.8cm wide. The Chain inlay bracelet is 1cm wide. All our COPPERVAST Therapy bracelets are adjustable with space of + or - 3cm. As copper is a soft metal you can easily press and adjust on your wrist to get the desired fit, so it can fit most of the wrists. We also have different variations where you can choose from. Please do not hesitate to contact me again for any other questions you may have. Thank you and have a wonderful day! Sincerely and respectfully.