If you want to have fun, volunteer to replace the idler gear bearings on a Jeep Dana 18 transfer case.
The idler gear is large, about a foot long. You lay in on the table with the large end flat down.
Place the 1-1/4 inch shaft down the center of the gear.
Drop in a flat washer that is a loose fit around the shaft and loose fit inside the gear.
Add grease, and carefully place 24 needle bearings down into the bottom of the gear with the ends resting on the washer.
Then, another flat washer, more grease, and another 24 bearings and then a final washer.
Then you carefully slide the shaft out.
Very carefully lift the gear up to horizontal and slide it into the bottom of the gearbox. Its a snug fit, and you line up the holes in the case with the holes in the washers.
Then even more carefully slide the shaft in through the case, past the first washer, 24 bearings, second washer, 24 bearings, the final washer and out the hole in the back side of the case.
Listening carefully for the delicate "click" of one of the bearings being pushed out the back hole and hitting the floor.
And you will almost certainly hear it at least the first time.
And probably the second and third times too.
I was so glad when an after-market company came up with a kit to convert it to two tapered roller bearings...........