GR 500 High-Vacuum Grease is a stiff, non-melting silicone lubricating material that maintains its consistency from –40°C to 225°C. GR 500 High-Vacuum Grease is recommended for vacuums reaching between 1 × 10–5 and 1 × 10–6 mm Hg. It is recommended that the grease be preconditioned under vacuum and temperature until these limits are reached.