What is this black hex screw?

A really useful resource when getting into doing mechanic work is being able to pull the manuals and parts diagrams for your components. You’re already 80% of the way there by just knowing your component, its trim level (Ultegra) and the number.

The next thing you’ll want is si.shimano.org:
[https://si.shimano.com/en/](https://si.shimano.com/en/)

If you plug in your component into the search bar you will find an “EV” – Exploded View, “DM” – Dealers Manual and “UM” – Users Manual.

Users Manuals are totally useless. mostly broad strokes like which part of the bike is the brakes, and disclaimers required by law or by lawyers i.e. “Don’t ride your road bike on gnarly single-track and then try and submit a warranty claim”

Dealers Manuals have important information about compatibility- like this derailleur can only support a cassette of a specific size range. Also step-by-step instructions for installation or servicing.

Exploded Views are an complete breakdown of all the small parts of every single thing Shimano makes, including the necessary replacement numbers.

The Ultegra ST R8000 is here:
[https://si.shimano.com/en/ev/ST-R8020-4245](https://si.shimano.com/en/ev/ST-R8020-4245)

The Dealer manual (And installation instructions are here:
[https://si.shimano.com/en/pdfs/dm/RADBR01/DM-RADBR01-11-ENG.pdf](https://si.shimano.com/en/pdfs/dm/RADBR01/DM-RADBR01-11-ENG.pdf))

It’s a bleed port. “Aka Bleed Screw and O-ring”