This is a brass T Fitting for hydraulic brakes. A common use for this brake fitting is on boat trailers, but of course it can be used on any trailer that has hydraulic brakes. This fitting is normally attached to the trailer axle and splits the main line that is coming from the master cylinder down one side of the trailer frame. The T-Fitting allows a short brake hose to reach the near side brake caliper or wheel cylinder and a longer hose to run the length of the axle to the other sides brake caliper or wheel cylinder. This is a high pressure fitting rated for drum or disc brakes using surge couplers or electric over hydraulic units. The ends are brass female 3/16" inverted flare fittings that use a 3/8-24 thread.