TromboneChat

My school has a bass trombone (Bach 50b I think) that I'm playing on and it works most of the time but sometimes the linkage on the 2nd rotor pops off from the actual rotor because it is missing a screw and I'm trying to figure out what the screw is called and where I can buy it. I will attach a picture of what I'm talking about (Note: this is not that same instrument. this is just a random picture I took from Google. the actual screw is a flathead)

What is written on the backing plate of the valves? Is it O.E. Thayer, or Orla Ed Thayer? Though I think those should be identical.

That is usually called a "stop arm screw", as it secures the stop arm to the valve spindle.

Yes a "stop arm screw"

Should be readily available through a tech, or try Hickeys Music

It is hard to imagine that any of the valve makers would go out of their way to use some kind of unusual screw, remove the one screw that you do have, take it to a hardware store, which has those little boxes of unusually sized, nuts, screws, washers, etc., and find a match, to make sure it’s the right match, find a nut that attaches to both the screw you brought with you, and the one you think is a match

Just FYI the thread size is

4-40

Bonearzt wrote: Sun Feb 08, 2026 12:49 pm Just FYI the thread size is

4-40

That should make it easy. If you don't have a hardware store handy, you can get it from Amazon. Yeah, you may have to get a bag of 10 of them for $5-$10. But that still may be less expensive overall than going to the hardware store and getting one or two, or taking it to a tech and having it done. That's how I have about 90 nylon cheese head screws -- left over from replacing/upgrading my valve guides on the 1924 Buescher tuba..