Abstract: A lock down apparatus for use with an oil well pumping unit of the walking beam type. It includes upper and lower clamps for attachment to the walking beam and to the bottom frame of the unit, respectively, and an adjustable tensioning arrangement extending between the two clamps. Part of the tensioning unit is a wire rope with plastic buttons pressed onto the rope at suitably spaced intervals. A coupler for latching to the particular button which is selected for adjustment for the distance between the walking beam and its frame is provided. Once the tensioning unit is in place, a turnbuckle is tightened to increase the tension to hold the walking beam in a lowered position, against inadvertent release of the pumping unit safety brake.