When procuring a Hydraulic Mono Jack, the most critical factor is the rated tensioning capacity (tonnage), typically ranging from 20 to 30 tons for standard prestressing tasks. You must verify the stroke length (usually 200mm or 250mm) to ensure it meets your specific elongation requirements. Additionally, check the wedge compatibility; the jack must match the diameter of your PC strands, commonly 12.7mm (0.5") or 15.24mm (0.6"). High-quality units should feature hard-chrome plated pistons to prevent corrosion and wear during high-pressure cycles.