When sourcing hollow hydraulic jacks, you must prioritize the tonnage capacity (ranging from 10 to 100+ tons) and the center hole diameter, which allows for the passage of bolts, cables, or shafts. Ensure the stroke length meets your specific lifting or tensioning requirements. Additionally, check for hard chrome-plated plungers to resist corrosion and wear, and verify that the sealing system is rated for high-pressure environments (typically 700 bar/10,000 psi) to prevent oil leakage during heavy-duty operations.