The Shure URT2 is the correct rack tray for mounting two Shure PGX4 wireless receivers. In fact, the Shure URT rack tray is also compatible with PG88 and PG4 receivers as well as P6T and PA765 antenna combiners. You can mount any two units into a convenient 1U rack space. The URT is also compatible with older Shure wireless receivers, including LX3, LX4, SC4, T4N, T4, UT4, and UT4A receivers. Holes in the bottom of the URT allow for permanent mounting of receivers.