One topic that comes up occasionally talking to other hornists is that of slide inserts on the horn.
Slide inserts are made from cut off bits of slide tubing, such as seen here. What you do is take the inserts and put them inside the slides to the point that the slide is pulled out where you want it. The idea is it acoustically smooths out that area, so there is no widening of the tubing diameter of the horn in the area where the slide is pulled out.
So for example let’s say the slide is pulled 1/2 inch. What you do is cut two slide tubes that length, put them down in the slides, then put your slide it. What it does is make a more consistent tube inner diameter through the slide.
So why would you want to bother? It would be to correct some issue of intonation or response on your horn. The theory is that a node must be is hitting at a bad place to cause the intonation or response problem, and inserts smooth the area out.
To remove the inserts you will probably need to use something like a small screwdriver or a metal rod. It is a good idea to remove and grease them with slide grease periodically if you use them for an extended period of time.
I used inserts from time to time on a couple horns I have owned. The most common reason to try them is to fix a bad high B-flat, on some older horns especially this note can have a bad “roll” that makes the note speak badly. I talk about this a bit more in this article.
Do they really help? Maybe. It is certainly something that you can try if you have a few notes you fear more than others due to the horn itself.