new unused surplus Hydraulic items from a local distributors overstock. This Particular unit is a M4SD-138-1N00-B501 denison hydraulic motor. this is a size. Pressure 2500 continuous psi / 3000 intermitent, 4000 max rpm at low load. for all details and specific speed v/s load curves go to the link below for the data sheet. http://www.denisonhydraulics.co.uk/Sales%20Literature/vane/BulSalesENM4.pdf
see second picture which is a close up of the nameplate.