So, I don't know how I did it, but I have stuck the thumb screw on the paddle for the second valve on my YBL-612. I don't recall super tightening it, but I can't get it unstuck with a rubber mat, and I don't want to break it. The thumb screws are literally the same screws Yamaha uses for lyres.

What tool/techniques would be best? Plastic Tip Pliers? Rubber tip pliers?

Try a drop or two of penetrating oil, might help. Doesn't need to be a brass instrument-specific product.

Oil certainly won't do any harm, but in that sort of 'dry' position it's more likely to be mechanically stuck (the screw tip makes a divot in the lever, and then any subsequent shifting adds a radial load) than especially corroded.

Time for nylon jaw pliers, or appropriately-sized normal pliers with a piece of firm leather wrapped around the screw head so you don't chew it up or strip the knurling.

Support the part so you don't bend the lever at the same time, and think about where your tools would follow through if you got carried away. Bell section on a table or between your knees, not on a stand with the slide still attached...

(If you're extremely unlucky and the head shears off, well, that was inevitable by the time you started.)

I've got lots of tools, but one of my favorites (little-used but indispensable when you really need it) is a plastic-jaw slip-joint pliers such as one of these:

<LINK_TEXT text="https://smile.amazon.com/PH-200-Non-mar ... 820&sr=8-3">https://smile.amazon.com/PH-200-Non-marring-Plastic-Touch-Pliers/dp/B000ALF5EK/ref=sr_1_3?crid=K3P3F06HQ3B6&keywords=non-marring+plastic+jaw+soft+touch+slip+joint+pliers&qid=1651078844&sprefix=IPS+PH-200+Non-marring+Plastic+Jaw+Soft+Touch+Slip+Joint+Pliers%2Caps%2C820&sr=8-3</LINK_TEXT>

<LINK_TEXT text="https://smile.amazon.com/Igarashi-PH-16 ... B000ALF5EK">https://smile.amazon.com/Igarashi-PH-165-Non-marring-Plastic-Pliers/dp/B001V7DYSQ/ref=psdc_553324_t2_B000ALF5EK</LINK_TEXT>

[quote="Posaunus"]I've got lots of tools, but one of my favorites (little-used but indispensable when you really need it) is a plastic-jaw slip-joint pliers such as one of these:

<LINK_TEXT text="https://smile.amazon.com/PH-200-Non-mar ... 820&sr=8-3">https://smile.amazon.com/PH-200-Non-marring-Plastic-Touch-Pliers/dp/B000ALF5EK/ref=sr_1_3?crid=K3P3F06HQ3B6&keywords=non-marring+plastic+jaw+soft+touch+slip+joint+pliers&qid=1651078844&sprefix=IPS+PH-200+Non-marring+Plastic+Jaw+Soft+Touch+Slip+Joint+Pliers%2Caps%2C820&sr=8-3</LINK_TEXT>

<LINK_TEXT text="https://smile.amazon.com/Igarashi-PH-16 ... B000ALF5EK">https://smile.amazon.com/Igarashi-PH-165-Non-marring-Plastic-Pliers/dp/B001V7DYSQ/ref=psdc_553324_t2_B000ALF5EK</LINK_TEXT>[/quote] Nice! I went for the PH-165. Looks like if I really want, I can get different pads for them too.

Part of the problem is that can't really get a good grip on it, even with the rubber mat. It can feel it just stretching under my finger and thumb.

I also will definitely be careful on what I use for leverage. I don't want to bend the linkage or the paddle.

[quote="ithinknot"]Support the part so you don't bend the lever at the same time, and think about where your tools would follow through if you got carried away. Bell section on a table or between your knees, not on a stand with the slide still attached...

(If you're extremely unlucky and the head shears off, well, that was inevitable by the time you started.)[/quote] I got the Nylon tipped pliers today (yay amazon), and it was honestly easy. The thumb wheel moved without much effort, but i couldn't move it with hand strength until it went around almost an entire revolution.

I also was able to use it on the F-paddle on my New YBL-830, which also was stuck. I guess I just need to be careful about tightening them too much. Maybe it was cold when I tightened them, and it's warmer now?