Parker A-Lok 4SC4-B Brass Compression Tube Fitting, Union, 1/4" Tube OD Dual couplings for joining two tubes of the same diameter Solid brass construction for durability and resistance to corrosion Back ferrules hold tubing tight within the body of the fitting while front ferrules hold tubing tight through the nut Compression connections on both ends to provide a leak-proof connection without the need for additional joining preparations Capable of joining a variety of tubing materials such as stainless steel, copper, and rigid and semi-rigid plastics and polymers