Further to my first (and preliminary) post above .......
The Glacia is quite a nice looking Ballpoint pen (BP) when fully assembled, and I respect Berea quality.
There is some ornamentation on the top of the finial.
There is some attractive ornamental engraving (blackened) on a ring that fits below the finial and completes it.
The refill operation is a finial twist mechanism.
The nib is rather long with the exposed portion being ... 1.328" long and is tapered with maximum diameter of ... 0.433" (matching the bushing).
The nib has an integral threaded stub which screws into another short brass stub piece which, in turn, presses into the brass tube.
It would seem that you can do refill replacement either by unscrewing the nib, or by pulling off the finial and unscrewing the transmission.
(or just unscrew finial plus transmission together, if appropriate).
Just did this little bit of research on the Glacia kit (made measurements on actual unused kit in my possession)....
Recommended drill size is ... 17/32" = 0.344" (actual tube diameter measures as ... 0.332")
Smaller of the two bushing size = ... 0.433" at nib end
Subtracting and dividing by 2 gives wall thickness at nib end of : ... 0.5 x ( 0.433 - 0.344) = ... 0.0445"
So, the wall thickness at nib end is ... 0.0445"
I was close, but a little off ... it's not quite as thin as I said in my first post above.
@Wayne
If you read this, could you please enter the Bushing Sizes in the Berea table as : ... Smaller (nib) = ... 0.433" and Larger (finial) = ... 0.469"
The stubs on both bushings (inserts into brass tube) measure at ... 0.313" diameter.
The tube diameter is ... 0.332" ... as already noted, and the tube length is ... 2.581" ... in case you need those numbers also for complete info.
Thanks,