Taking apart rear axles for parts recently, I've found a few of the thousands of aftermarket parts made for Model T's. Here are three versions of the same thing, end caps.
This is the simplest, just a press-on collar and a disk with a hole for the axle. It used the regular felt seal and washer.
This one's about the same but has the bolt to clamp it on.
I take this fancy thing to be fairly recent.
"GREASTITE PAT. APPL'D. FOR T. & A. MFG. CO. ST. PAUL, MINN."
Inner cap, leather seal & spring, clamp-on outer cap.
Here's a NOS one I posted a while ago under accessory of the day