1/2-in Female Pipe x 3/8 Male Flare Brass Fitting
This is an adapter which lets you shrink a 1/2 inch male to a 3/8 inch male. It has various uses in grilling but usually it, somehow, connects your grill to a propane or natural gas source. The adapter can connect to a copper pipe, a black rubber hose, a Flexo of whatever gas line you have.
The model number 46EF is a generic number used by several manufacturers who make this same product.
connects grill to gas.