Tektro HD-R210 bleed port adapter identification

It's possible someone might randomly know, but for the most part that's not how this game works.

Bleed fitting typology on random OEM type hydros is chaos. There are no resources. It's not all the same within brands. It's figured out by having a variety of options when you crack it open.

When you take out the bleed screw, look at the diameter, pitch, threaded length, presence or absence of an o-ring, and shoulder profile. All you're trying to do is find a fitting that's a match. Usually in a nice completist set like this, something is going to match exactly. Assuming you're doing a two-syringe bleed, where you skloosh the fluid back and forth until no more bubbles come out, you'll do the same for the lever end. (This method works best for most Tektro brakes in my experience despite how their basic consumer bleed kit only comes with one syringe.)

Some Tektro caliper fittings don't have an o-ring and may not seal right if the syringe fitting you attempt to use has an o-ring. So if you run into sealing problems, remember you can take the o-ring off a fitting you have to create a match.

If by some chance you open a bleed port and find you don't have a match, it's true that's not ideal and it's theoretically possible to introduce air and find yourself in worse shape then when you started, but in practical terms the other end being sealed is going to keep the bulk of the fluid in, so all you're likely to lose is some droplets right at the opening. You can carefully drip a little oil back in and seal it up and there shouldn't be much change if any.

Take heart that the ironic thing about bleeding Tektros is that despite lack of clear written procedure, it almost always works out fine if you just do it. Over the years I've come to postulate that that's why the written procedures are so bad; they seem like an afterthought because they probably are.

I'd just try all the fittings that seem like a match. Just be careful not to force anything, the right fitting will thread on without effort. Go for a funnel bleed, or even better a gravity bleed. Using two syringes is unnecessary effort.

You already have the answers you need. I'm going to add for completeness that (especially the rear brake on) most Tektro hydraulics I've encountered, they feel like they need bleeding when the pads are worn past a certain point. Resetting the calipers and replacing the pads solves the problem, where resetting the calipers, bleeding properly and reusing the old pads puts you back where you were before you started.

They are still good brakes for the money.