Thread on a threaded 16g co2 cartridge. Press the control valve onto your tubes valve stem. Open the control valve slowly until you hear air go in, then open the valve all the way. When your tire is inflated turn the control valve shut. I used this in my garage for practice. First time on the road, I went kinda brain dead. I forgot to turn the valve off after my tire was inflated. I lost a little bit of air. Second, it was a cold day and the control valve stuck to my presta valve and I had to yank it off.
It comes with a sleeve to put on a cartridge so your hands won't get frost bite and stick to the co2 cartridge (ouch).
Only downside is that is takes two hands to use this. You have to lean your wheel against something, or put your wheel on your bike and tip it upside down, then you can use two hands. Just make sure your tire is completely seated. Another thing is this thing is so small I worry about losing it.
Kinda pricy for it's size. But it's worth it when you are standing on the side of the road with a dreaded F.
Very satisfied with size that easily fits in small saddle and easy to fill tire. Others I have had were cumbersome. Good price and shipping...bought another for our mountain bike.
I like this because (1) it is reasonably small so it fits nicely into my saddlebag, (2) being able to regulate the CO2 flow is a plus, (3) the neoprene sleeve keeps you from freezing your fingers to the CO2 cartridge when it gets cold as the gas flows out, and (4) it's not too heavy. Hard to imagine what else one could want from an inflator. I got the opportunity to test mine when a 1 self-tapping screw threaded itself through my rear tire, tube, and inner surface of the rim the other day, and it worked perfectly.
I avoided ALL CO2 products because of a bad experience in the early evolution of these systems. I figured you can't go wrong with an old style hand pump. This CO2 inflator appears to be idiot proof. Believe me I would know. I would recommend this product in a heartbeat.