machine has both inner and outer seals, but also has an axle seal just inside the axle tube. the parts guys on quoted jobs don't usually include those seals in the job, and because the axles are heavy, the seals take a beating on r&r of axles. every truck of this type I've done brakes on, has had at least one previous brake job where the axle seals were not changed. a heel bar will get them out and the correct size socket as a drift and a hammer will install them. be careful not to hit them too hard when installing because the tube has a seat for them and you can crush them. hope this helps someone.