Aftermarket Part - Not Manufactured by Penn
Made by a machinist as per Alan Tani's specs.

Stainless steel gear sleeve (98-505AT) (Fine Tooth).
Recommend if you INTEND to exceed 8 pounds of drag (based on use in the 500 Jigmaster, but applies to any of the reels where you want to apply more drag than originally intended).

See Pennparts.com section on Conv. Photo Walk-Thrus for articles/notes by Alan Tani.

About the two different runs of 10-505 drag stars

This was discovered 4/2012
It is not related to the fine-toothed thread info above. It is a separate issue.
Penn did a more recent manufacturing run of these 10-505 stars.
They changed the machining of the fine thread just slightly enough to cause an issue with the newly made stainless sleeves, as described in the photo notes below.

SIMPLIFIED

If you only intend to use the 98-505 brass gear sleeve, order 10-505-B.

If you might, or are, changing to the
98-505AT stainless steel sleeve, order 10-505BS that fits both.