I drive a tractor trailer and we know how handy this type of pneumatic machine is. Decided to order this one. I had to inflate all the tires and found that the rear-facing cartridge wasn't that good. It needs to be tighter to snap onto the valve stem. It seemed that the userid was too big. But the front cartridge held on to all air valves with no problem. I've found what appears to be a much better air chuck screw head online, but I want to see if they will send a replacement head for it and it might just have been a defective head.