I bought a Shimano small part called "EW-SS302 Lockring WH
Magnet and Washer" for myself.
This part isn't the EW-SS302 itself.
Shimano has a STEPS
assist unit series for e-bikes, and within that series
there's an EW-SS300 wired speed sensor
(I think SS stands for speed sensor),
then its successor model EW-SS301, and
even further down the line is the EW-SS302,
and this is the magnet-side component of that sensor.
The part number is
Y1XL98010, as shown in the image above.
The "WH" in the product name isn't a color code
meaning white, but rather stands for "with,"
The washer that prevents excessive biting from the teeth
is also found on sprockets and center-lock
lockrings, but
this center-lock internal-threaded lockring
has a magnet embedded in it
for the EW-SS300 series wired sensor.
The round seal sticker wasn't applied cleanly at the edge, so
↑I peeled it off and it looks like this
probably didn't anticipate, so I decided to buy it.