MO-4 HF Mobile Antenna Mast for Deck or Roof Mount, designed for Hustler HF Resonators The MO-4 is designed for use with Hustler mobile H.F.resonators The performance of the MO-4 is slightly less than that of our full size 54" mast. The MO-4 is constructed of a solid stainless steel rod with 3.8-24 fitting on both ends.