They didn't have flow-thru when I originally got the system, so non-flow thru for coach and toad. But in reality, I very seldom have to add air, so really a non issue. TST does say you should have metal valve stems, a must for the flow-thru, suggested for the caps. I do have metal stems on the 6 on the coach, but just standard on the toad, and have not experienced any issues. If you remove the anti-theft caps, the actual sensor is really pretty small. I had asked if I needed to re-balance my wheels after adding the sensors and was told no. Haven't experienced any shake or shimmy with them in place, either. ST