The sealing ring for the UPR hole is the main seal for the plug hole made of NBR rubber. Because it is a one-way design, two backward-facing Settings are used when dual action is required. The low temperature type NBR rubber option is available for use in extremely cold areas. The friction resistance is small, which can reduce the crawling phenomenon in the compound movement. Static sealing effect is remarkable. The notch design on the back of the lip eliminates pressure accumulation between the sealing rings.