The FMJ by MAD Industries will revolutionize the authentic mechanical mod industry. The FMJ authentic mechanical mod comes with its own RDA housing which will fit many of the 25mm RDAs on the market. The RDA housing comes with a 1/2 inch wide bore drip tip and O-rings. The design of the RDA housing allows you to use your RDA base & atomizer without having to worry about the O-rings . The housing fits over your RDA and has its own O-rings. It has its own 1/2 inch bore tip that is one piece with the housing and it comes with MAD Industries originally designed concave button so that no locking mechanism is needed.