Stucki hydraulic stabilizers are the only hydraulic damping units guaranteed to meet AAR Specification M-965, AAR Field Manual Rule 50 and Rule 88 to ensure safe operation of the freight car while controlling resonant rocking of high-center-of-gravity cars with D5 or D4 springs. The Stucki HydraShox™ products utilize a high pressure seal which provides superior performance and life while preserving oil reserve levels. This fluid loss is compensated for by the reserve oil. The Stucki HS-7 and HS-10 incorporate a low pressure seal on the piston rod, which may pass slight amounts of oil under normal operating conditions.