This double-over-double spring balance design employs twin bank torsion springs for maximum counterbalance capability. To accommodate varying heavy weight assemblies, the uppers and lowers can be constructed with combination sets of ‘D’ and/or ‘P’ main springs to carry the operational load in a balanced condition.
In/lbs. of torque output at 100° deflection
·  645-DC offers 12,000
·  645-D/PC offers 16,000
·  645-PC offers 20,000