Usually the diameter of a wand is 5/16 or 3/8. Having a 4g P.A. you will need to measure from the end of the penis to the P.A. hole as that is where the threaded stud is placed to hold the wand in. As far as wearing the wand for twelve hours, I would suggest that you wear it on days that you are not working until you decide how long that you are able to have it in. I hope that if you have a 4g cbr that you have a ring removing tool.
Wait till you are in a hurry and take a whiz with the end ball still screwed in. OOPs

I know a guy who wore one for several hours straight and he regretted it! His urethra stuck to the wand and ripped while removing it. He ended up being catheterized for 2 weeks while his urethra healed and eventually had to have a stint surgically installed to keep his urethra open. Scar tissue became a real problem for him.

All because he didn't heed my advise to use his wand for short term PLAY only. Also, he used water-based lube which absorbed too quickly...instead of petroleum like he was told.

Also, there's a measuring guide that I wrote for Tribalectic somewhere on this site. If you can't find it, ask drew@tribalectic.com, he'll make sure you find it.

Thanks for the info! I was wondering about length, I am a grower not a shower, so mine kinda shrinks away during the day, and I was thinking if a shorter wand would wear better for a longer period of time.

*cringe*

I have a shorter wand (2" between crosspin and the internal end) and have worn it all day. I think no matter what, that metal end is going to irritate your urethra wherever it terminates. I was thinking of maybe buying a very short one (probably equal lengths both sides of the crosspin), but haven't yet. A bar that short won't go too far down your urethra and may be subject to less irritation.

My (hollow) prince's wand is great for stopping the spray! Except the bore of the hole is very large, and it doesn't sound "normal" when your pee hits the water...

wow - they would be hot to wear for play time i think, but all the time - hmmm scary?

Since Wands are intended for play and not long-term wear, I'd suggest you play with some sounds first http://en.wikipedia.org/wiki/Urethral_Play and see what sort of depth is a turn-on for you.

Then older a Wand that fits within your comfort range.