Sintered metal bushings soaked with oil. Chrysler invented them around 1930. Trademarked name is "oilite". A very popular product for many decades, probably

Sintered metal bushings soaked with oil. Chrysler invented them around 1930. Trademarked name is "oilite". A very popular product for many decades, probably some in your car or house today. It really blows some peoples minds when what looks like a block of solid bronze soaks up to maybe a fifth its volume of oil. For something thats 20% hollow its also remarkably strong. Its an example of a piece of technology that depends on numerous contemporary things. You need razor sharp cutting tools to keep the pores open, so it has to be a "post-carbide" era tool. You need a vacuum pump to fill the pores with oil. You need modern non-drying low acidity mineral oils because something like veg oil or whale oil would break down both the bearing and the shaft in a couple years. The powder is heated precisely and under some pressure, a lot more precise than a blacksmiths shop. Speaking of pressure, reproducible and reliable sintering seems to always require some amount of pressure, which is a problem for 3-d printing, either you're using somewhat exotic process, or the product needed pressure so it is going to be weak.