Screw on deflator (aspirator) for use on TR218 air/water tractor tube stems and large bore stems such as those found on road grader, dirt scraper, loader, and other large industrial tubes. NOT FOR STANDARD VALVE CAR OR PICKUPS! On tractor tubes it screws over the external rim nut threads of the TR218 air/water stem base. On large bore industrial tubes you must remove the large bore valve core and then it screws over the external cap threads of the stem. It uses moving air to suck the tube or tire flat. It works on the venturi principle, you pass air through it using a standard air chuck. A clip on chuck works best so you don't have to hold the chuck on it the whole time. This is great for sucking tubes flat after patching to ease reassembly of the tire and tube. Also comes in handy in freeing tubes that are stuck to the inside of the tire. Can also be used to suck a mounted tubeless tire flat on the wheel to make it easier to start your hand bead breaking wedges.