When the housing is split you can install the seal in the housing part and use it as mounting tool. It must be mounted perpendicular to the housing bore axis. When installing seals on stepped shafts, where the shoulders do not have the recommended chamfer or rounded transition, an installation sleeve (fig 4) must be used. If the sealing lip has to pass over grooves, threads or gearing, thin-walled installation sleeves can be used to prevent the lip from being damaged. The outside surface of the sleeve should be coated with the same lubricant that is used to lubricate the seal and counterface surface. Radial shaft seals made of silicone rubber should always be installed using an installation sleeve.
More technical specification: https://www.skf.com/group/products/industrial-seals/power-transmission-seals/radial-shaft-seals/technical-specification
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