All About Cock Rings
A cock ring literally is a ring. It can be made of various materials: stretchy rubber, jelly rubber, silicone, neoprene, cloth, leather, or even metal (though i wouldn’t recommend the last two for your first cockring because they can be uncomfortable or painful). As the name implies, cock rings are meant to encircle the penis and often the testicles as well.
A cock ring can be used to restrict the flow of blood in a penis, which can help a man attain and maintain and thicker and harder erection, as well as delay his orgasm. (However, it is advised that a cock ring be removed before ejaculation to enhance the orgasm and avoid problems.)
I would suggest the softer rubber rings because they restrict the blood flow without causing any damage to the tissue. 
Another, more equitable use for the cock ring is for the stimulation of your partner’s genitals as well as your own. Jelly rings are made to give you to option to wear them higher up on the shaft of the penis and often have knobs or spikes for stimulating your partner. Some rubber rings have ticklers affixed for clitoral stimulation and some even come with a vibrating attachment!
Using a cock ring alone or with a partner can be a simple way to spice up your sex life. But 
remember that the cock ring can be dangerous if not used correctly. A cock ring that fits over the testicles should be taken on and off very carefully. It is also important to ensure that you have the right sized ring to prevent tissue damage. To find the diameter of a snug fitting ring, measure the distance around the penis and testicles (at the base, behind the scrotum) and then divide by 3.1. Don’t go smaller than that.
I also don’t recommend snapping the ring while you are wearing it, since that could be rather painful. ^_~
Posted: November 25th, 2004 under sex toys.
Comments
Comment from Shay
Time June 25, 2007 at 1:53 am
No, it is not safe to wear a cock-ring all day. It’s not good for the tissue and, even if you’re using a non-compressive ring, it’s not so good for the skin. You could permanently damage your penis and since you only have have of those, don’t risk it!
Comment from Anonymous
Time August 29, 2007 at 11:32 pm
So I guess you could do this while you are masturbating, without the ring, just using your fingers? I am a sex n00b, so, I art curious.(And yes I’m over 18 =P)
Comment from Shay
Time September 7, 2007 at 1:02 am
yeah, I suppose you could - though you might end up too distracted to keep it up (the action, not your penis) ^_~
Comment from Anonymous
Time November 12, 2007 at 5:23 am
When you say measure, measure in what? inches, cm, what exactly?
Comment from Anonymous
Time December 14, 2007 at 1:20 am
What about the Jelly Rings?? I like to wear it a long time. LOve the way it feels and does not bother me at all. Can I wear it all day if I monitor the way it feels on me??
Comment from Shay
Time January 14, 2008 at 5:38 am
If I were you I wouldn’t risk it.
Comment from Anonymous
Time June 22, 2007 at 7:14 pm
Is it safe to wear the cock ring all day? I like the way it feels, and do not mind the erection all day. I have the jelly ones for less tissue problems, and wnated to know if it was ok to do so.