Welcome to the site..

The rims are missing the ‘Center caps’ Not sure who’s rims those are, but generally they can be measured out by the hole diameter and an aftermarket cap bought or sourced. Or possible still available from the manufacturer of the rims, maybe not the same design given their age, but would fit.

But the images descriptions seem wrong,, here’s why..

The image that shows the small cap protruding should be L/R front wheel/s and the small cap you see is a dust cap over the wheel bearing/wheel nut to protect the bearing from water and debris. Some call them grease caps, bearing caps etc. If a dust cap were missing up front, you’d see a large nut with a cotter pin (locking pin) through it.

The image showing a more open hole in the rim,, you can see an ‘axle face’ in the diameter opening would be rear wheels as you noted. The rear axle doesn’t have a dust cap, it’s completely sealed off and flat looking. So, normal..

With the rims Center caps missing, it doesn’t create any issues other than appearance...

“Although” the dust cap in that image is damaged showing a hole on its face, and a distorted or flattened area around the caps circumference, both points for intrusion. At the very least the cap needs to be replaced, but if it’s been open to the elements (water/dirt/rust etc) for a long period of time, might be a good idea to check the bearings. Once the cap is removed, if there’s evidence of rust on the caps interior, the nut and washer you can see is rusted, or collected water on the inside, dirt etc it should be disassembled and inspected. May need to wash out the bearings, repack them in fresh grease and a new hub seal if need be, and of course a new dust cap. If bearings were rusted, pitted, then bearing replacement done as part of the service.

The small dust cap is just a lite press fit, so to remove it you can get a wide flat blade screw driver under the lip at its base and pry it loose, or grab it with a pair of channel locks and walk it off. They dent easily (can see that in the image as well) and there’s actually a tool to remove them, but either noted work to remove them. To install,, gently tap back in place with a rubber mallet.

We can help with instructions if needed...