This exercise presents a unique challenge to the triceps...it's a two-arm-looking one-arm movement. Yeah, I know that just sounds nuts.
Even though you'll have two hands on the bar, only one hand is going to actually be supporting the weight...the other hand will just be there to balance the bar. And this is in EXTREMELY effective for working the triceps hard and in a very focused manner.
I've found this to be really effective if you have one arm stronger than the other and barbell training tends to make that imbalance worse. I've also found this to get a better feel on the triceps than doing it with just a single dumbell - the barbell still locks the arm into the movement better while still allowing that single arm focus.
It's kind of the best of both worlds.
I prefer to do this exercise lying on the floor - it's MUCH easier to get the bar into position and you can do the exercise by yourself without having to worry so much.
Use a weight that you would ordinarily be able to get about 15+ reps with on a two-arm close-grip bench press with the EZ bar (or if you have a small straight bar, that'll work, too). I've got a couple of 25's on the bar here.
Lay down on the floor then reach back and do an extension with the bar to get it into position at the top of the press movement. Your hands should be fairly close together on the bar (closer than usual for a press). This is important for balance when shifting your hands on the bar.
Note how I've moved my left hand into the very center point of the bar in the next picture here (while the right hand stays close by for balance).
Now slide your right hand wide out to the side, out by the plate. The weight is being supported almost completely by the left arm, with the right arm acting like a outrigger on a canoe and balancing the bar (hence the name).
Then lower the bar, keeping your left arm in close to your body. I did this a floor-press style movement where I actually rested my arm on the floor to take tension off and force a full tension-free start at the bottom. You don't have to do it this way, but it makes for a good challenge!
Then just press back up, keeping that right hand balance the bar.
When you've finished your reps on the left arm, bring your right arm back into the center, shift your left hand over a bit, then get your right hand into the center point.
Now it's the same deal with the right arm taking up the whole weight.
It looks like a strange exercise but it really is a one-arm two-arm-looking press movement. Pretty much ALL the resistance gets placed on one arm at a time.
It is important to start with a light to moderate weight the first time you do this one, because it is a one-arm movement, pretty much and because of how you'll be shifting your hands on the bar. Be VERY sure you're comfortable doing this. If you're not, get a spotter to hold the bar up when you shift your hands.
This one will KILL your triceps.