Here are some details about the product:
Unstretched length, 5", can be stretched out to 20" with little hassle
Unstretched diameter of hole, 1/2". Can be stretched out to about 5" with little hassle, so this will accomodate even the largest men out there.

The masturbator is a hollow tube all the way through, unlike some other products in this category. This has 3 distinct benefits:
1. It feels excellent sliding the end opening up and over the head, and back down again.
2. As it is hollow, it is possible to slide the tube down, as in the product picture, to ensure that when you cum nothing gets inside the tube, making for easier cleanup (especially if there's a mouth waiting).
3. Due to its stretchy nature, it is possible to accomodate two people, one from each end, for an interesting experience.

Looking at the picture you can see a lot of ribbing, this does not carry through to the inside, which is (mostly) smooth. However, it is stretchy enough to turn it completely inside out, giving a slighter tighter squeeze and ribbing on the inside. Being able to turn it inside out also makes it very easy to clean up any lube or other liquids from inside the tube.

This tube does need to be used with a lubricant of some sort, however I have found that a generous gob of saliva will do the trick, and you may even prefer it if you are after a rougher experience.

For $15 I think this is an absolute steal, you won't regret it.