Originally Posted by
smd4
Don't know why it would be for grease. Why would you want to fill your entire headtube with grease? If it's threaded, just screw in an appropriately-sized bolt.
Oldschool thinking, I've seen a few older frames with them, oil seems to be the likely choice, pretty sure some did get filled with grease.
Here's an old discussion.
What's the use for this bolt on the back of the headtube?