ROHN's R-BAS25G bearing and accessory shelf is designed as a complete unit with top and bottom plate and integrated tubular legs. Rohn has designed the assembly to be compatible with its line of 25G standard tower sections and it is meant to me installed as the topmost section of the tower. The R-BAS25G is drilled to accept a thrust bearing (see the ROHN R-TB3 and R-TB4) on the top plate for use with an extended mast and the accessory shelf comes pre-drilled making it compatible with many of today's most popular rotor models.