To save time and effort on Silver Lake days, I put this together to try out. The basic idea is to tie all 4 tires together with air hoses and to air them all up or down at the same time. No repeated checks of pressure at each tire needed. Since my rig has pretty even weight distribution, equalizing them all to the same pressure is a good thing. You can buy things like this, but they seem kind of expensive, seeing as most of us have some of the parts laying around anyway. $115 and the gauge is extra? I think it's obvious from the pictures pretty much what is in the system. The key turns out to be the chucks. I picked up these at Harbor Freight and they DO NOT work for this application. The problem is with the self closing valve. That pintle just rattles around in there and relies on the compressed air to close it. So you can't air down with it - nothing will engage the schrader valve on the tire. I disassembled them and added some springs that I happened to have on hand. Where did they come from? How should I know? Where did these buckets of used bolts and old car parts come from? This allows airing up and airing down, but the valve and schrader take turns pulling in and out based on the feed pressure, which is quite annoying. So I made the pintle slightly longer with some solder on the tip. Now they work pretty much how I would want. You would think the ideal hookup would be the hose from a pistol inflator, but a "straight-through" design has other issues. Why do you need the self shut-off? Otherwise you can never equalize the pressure. As soon as you pull one off, the air from the other 3 tires leaks out as you run around disconnecting them. I also soldered up a little valve-stem type fitting to standard chuck fitting so I can air up from any standard tire-filling station.