I rarely work on aerometrics - usually vacs. I did not pay attention when I disassembled the feed and breather tube on an aerometic P "51". Does the end of the breather tube with the hole go down by the feed or on the other end? Thanks.

The lateral hole lies at the feed end.

Hmmmm, well, as my snippy and snide and totally unbecoming aside to those well-meaning but misguided souls who favor 51 Vacs, this is a telling admission, but no surprise to the true 51 "function over form" faithful.

Then again, with regards restricted to aesthetics, the blue diamond, gold filled clip of the earlier 51 Vacs beats the plain arrow clip of the Aeros all to hell. A frankenpen blue diamond cap on an Aerometric 51 is the true fusion of beauty and function. Well, JMO.

Yes, the small side hole in the breather tube goes toward the section end, to allow sac air expansion to escape out the nib without ejecting ink when the pen is carried clipped in the pocket (i.e., nib up).

Funny you would say this. The pen I am restoring is a signet which came with a blue diamond clip and an amber jewel. I'm restoring the clip and jewel back to the correct ones. I agree completely, however, that the blue diamond clip looked better!

Now, imagine the first edition (with gold cap band) 51 Flighter with an earlier 51 Vac blue diamond gold clip cap. The mind boggles.