This is a Brass T-Fitting that features a 1/8" ID and accepts the 3/16", 3/8-24 thread Male Ends from standard hydraulic brake hoses. The main purposes of the T-Fitting are for trailers operating a single axle disc brake system and for the rear axle on a tandem axle disc brake system. To clarify, even if you have a tandem (two) axle trailer, if you only using one axle for disc brakes, this would be the correct fitting. In addition, if you are using a tandem axle disc brake arrangement, this would also be the correct fitting for the rear axle. Most common Trailer Brake Hoses are Male/Male Ends, which is why most of the fittings are all female/female. This T-fitting accepts the main length of brake hoses coming from the front of the trailer, accepts the length of brake hoses running to the closest caliper, and accepts the length of brake hose running from the furthest away caliper.