What is this part that came with my eggbeater pedals? I bought some second-hand Crank Bros Eggbeater pedals. They came in the original box, apparently with all the bits except the cleats. (That's fine. CB cleats are effectively a consumable.)
One of the bits is a pair of plastic pieces I don't recognize. I'm still working on getting a photo from my phone in a place I can upload it, but in the meantime, please enjoy these ASCII drawings:
  ___     ,     ,       ___
 / _ \    |__   |__    /   \
( (_) )   |▓▓   |__   (  *  )
 \___/    |     |      \___/
 Front   Side   Side    Back
               Cutaway

Each piece is a plastic disc with a knurled edge. From the disc, a ring is extruded, with threading on the outside of the ring. The ring's inner diameter is 10mm, and the outside is ~13.5mm. The outside diameter seems to be the same as a pedal spindle diameter, but the threading has a different pitch. There's also a very small hole through the centre of the disc, so it can't be used to seal anything.
Without a picture it sounds like the grease port tool

This picture was found in this article on rebuilding eggbeater pedals.

The Crank Brothers Eggbeater pedals, however, require periodic lubrication. A maintenance interval of once per season seems to be the general consensus.
As the Eggbeaters come with a grease port attachment, I purchased a grease gun

Evidently Eggbeater supplies the fitting but someone there does not recommend using it.

It seems like a painless, 5-minute job: remove dust cap; install grease port attachment; squirt in new grease, wipe off the old grease (pushed out from the seals on the inboard side); reinstall dust cap; and you are done.
Call me anal, but I decided to double-check with the manufacturer — and I am glad I did:

Hello,
Thank you for your e-mail.
...we would suggest not using the grease port. We would rather you take the spindle out and  grease it like that. Just unscrew the endcap and take the nut  off -  then pull the spindle out and re-grease.
Hopefully this helps,
Thanks
Anka Martin
anka@crankbrothers.com
Customer Service
www.crankbrothers.com


Here is another article with slightly better pictures.