This is the first generation precision machined ALL METAL (aircraft aluminum) Acratech ultimate Ball Head.  A rare find for collectors or discriminating photographers who like precision tools.  The arca/rrs mount will segue with most brackets made today since the arca mount system has become the professional standard in our industry.  The head is amazing for macro setups as it has the ability to get the camera locked in at beyond 90 degrees in any direction.  Also a phenomenal field Head because you can use it in any conditions anywhere.   If it gets muddy just hose it clean.  Acratec made the first generation Ball head impregnable, a real tool with no deteriorating rubber handles, no corners cut, a very nice tool.  It's what gave them their start in the photo Ball head world.  This is a classic tool in minty condition with just a few marks, see my pictures.