This is the full size GP precision machined ALL METAL (aircraft aluminum) Acratech Ball Head.  A wonderful find for 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 travel, outdoors, wildlife and hiking.  Also a phenomenal field Head because you can use it in any conditions anywhere.  It even has the ability to work as a gimbal head with lenses like the 70-200mm f2.8.

If it gets muddy just hose it clean.  Acratec makes their Ball head impregnable, a real tool with nice rubber coated control handles, no corners cut, a very nice tool.  This is an excellent tool in nice condition with just a few marks, see my pictures.