TromboneChat

This has probably been asked before but I can't search the forum yet. Why are there small discrepancies between bore sizes for bass trombone (.562, .563 etc) when tenors are usually more standardized? Are outer slides incompatible if they are off by even .001?

I think it's simply a matter of rounding up or rounding down from .5625 which is 9/16 inch.
Plus, drawn tubes are not entirely accurate.

dewque wrote: Fri Apr 24, 2026 7:39 pm Are outer slides incompatible if they are off by even .001?

As far as being "compatible", the important dimension isn't the bore, it's the stocking OD and the ID of the outer slide (and .001" difference shouldn't be an issue there).

dewque wrote: Fri Apr 24, 2026 7:39 pm This has probably been asked before but I can't search the forum yet. Why are there small discrepancies between bore sizes for bass trombone (.562, .563 etc) when tenors are usually more standardized? Are outer slides incompatible if they are off by even .001?

Over the length of the tube, the diameter may differ by +/- 0.003" depending on the horn, age, repair status, etc. I don't know what the actual mfg drawings call for, but with the clearance involved, the process and materials involved, the type of motion expected and the length of the tubes, even 0.003 is going to be hard to hold. And then on top of that, you have the straightness to worry about. The tolerances would matter most at the stockings. In fact, the tolerances are the reason for the stockings. It is much easier to hold tight tolerances over a shorter space. I would be willing to bet that if you look at the actual manufacturing drawings, you will see different tolerances on the main part of the inner slide and the stocking. And I think you'd find that the actual controlling dimensions and tolerances would be applied to the outside of the inner rather than the inside.

And then when you have two pairs of slide tubes, you also have to worry about parallelism and distance apart (assembly tolerances on top of individual part tolerances).

Compatibility is more likely to be an issue due to center-to-center distance differences.

So it's safe to assume most basses are actually the same bore then? I'm aware slides are individually fit when manufactured so changing outers is not a good idea to start with, but it's interesting to learn about the actual tolerances involded. Thanks everyone!

I would venture that the .563 number you see from Yamaha is based on using metric rather than imperial tooling. 14.3 mm is 0.5629921 inches. This would also explain why there were old Yamaha large tenors at .551 bore rather than .547. .551 inches is 14 mm.

Is that also why Besson had that bass in .555?

According to the 2019 Allied Supply Catalog:

Stocking
I.D. O.D.
.560 .592 Bach 50B
.560 .595 King 6B, 7B, 8B
.562 .594 Getzen 1052, 1062 (upper slide)
.563 .596 Conn 71H, 72H
.564 .595 Yamaha 321, 322, 421

dewque wrote: Fri Apr 24, 2026 7:39 pm This has probably been asked before but I can't search the forum yet. Why are there small discrepancies between bore sizes for bass trombone (.562, .563 etc) when tenors are usually more standardized? Are outer slides incompatible if they are off by even .001?

Again, based on the Allied Supply Catalog, the bore size of the .547 trombones varies from .540" (Holton TR150) to .550" (King 4B).

wayne88ny wrote: Sun Apr 26, 2026 2:37 am

dewque wrote: Fri Apr 24, 2026 7:39 pm This has probably been asked before but I can't search the forum yet. Why are there small discrepancies between bore sizes for bass trombone (.562, .563 etc) when tenors are usually more standardized? Are outer slides incompatible if they are off by even .001?

Again, based on the Allied Supply Catalog, the bore size of the .547 trombones varies from .540" (Holton TR150) to .550" (King 4B).

The Holton for example, does this mean they built it in .540 but sold them as .547?

Possible change in design... or simply a typo. I guess you'd have to measure one or more to find out.

Those were measured at the stockings, could be some lip at the stockings making the measurement small.

dewque wrote: Sun Apr 26, 2026 9:09 pm

wayne88ny wrote: Sun Apr 26, 2026 2:37 am Again, based on the Allied Supply Catalog, the bore size of the .547 trombones varies from .540" (Holton TR150) to .550" (King 4B).

The Holton for example, does this mean they built it in .540 but sold them as .547?

dewque,
Suggest that you don't obsess about this. The few thousandths of an inch variation in bore size is not really important, unless you are manufacturing or repairing trombones. Bore size is just one of a plethora of variables that influence how an instruments plays / feels / sounds.

I once had TR150 and removed the stock leadpipe. Aftermarket 547 leadpipe did not fit in. I measured the stock leadpipe and it was 0.539~0.541 inch-ish so maybe indeed the TR150 was built 0.540" bore. I don't know exact manufacture year but maybe more recent 150s were built 0.547".

Posaunus wrote: Sun Apr 26, 2026 10:42 pm

dewque wrote: Sun Apr 26, 2026 9:09 pm

The Holton for example, does this mean they built it in .540 but sold them as .547?

dewque,
Suggest that you don't obsess about this. The few thousandths of an inch variation in bore size is not really important, unless you are manufacturing or repairing trombones. Bore size is just one of a plethora of variables that influence how an instruments plays / feels / sounds.

Definitely meant for this to be random nerdery, not practical advice

There have been other outliers. Olds O-25 tenor was .554 bore. Holton TR-159 was dual bore .547-.559.

Doldom wrote: Sun Apr 26, 2026 10:47 pm I once had TR150 and removed the stock leadpipe. Aftermarket 547 leadpipe did not fit in. I measured the stock leadpipe and it was 0.539~0.541 inch-ish so maybe indeed the TR150 was built 0.540" bore. I don't know exact manufacture year but maybe more recent 150s were built 0.547".

Stock .547 leadpipes measure considerably less than .547. If they were exactly .547 OD they wouldn't fit in a .547 slide tube. There has to be some clearance.

brassmedic wrote: Wed May 13, 2026 12:31 pm

Doldom wrote: Sun Apr 26, 2026 10:47 pm I once had TR150 and removed the stock leadpipe. Aftermarket 547 leadpipe did not fit in. I measured the stock leadpipe and it was 0.539~0.541 inch-ish so maybe indeed the TR150 was built 0.540" bore. I don't know exact manufacture year but maybe more recent 150s were built 0.547".

Stock .547 leadpipes measure considerably less than .547. If they were exactly .547 OD they wouldn't fit in a .547 slide tube.

Yes, maybe the TR150 inner slide was a little bigger, like 0.542 inch..? But it was definetely smaller than 0.547 inch because your largebore pressfit leadpipes didn't fit in. By the way you made me special 8H nickel leadpipe that fits my TR150 some time ago. I sent you the spec of (very) approx OD of stock TR150 pipe and you made me smaller OD version of normal largebore pipes. It fitted very well and I enjoyed the pipe.(But I sold the horn eventually.)

Doldom wrote: Wed May 13, 2026 12:39 pm

brassmedic wrote: Wed May 13, 2026 12:31 pm

Stock .547 leadpipes measure considerably less than .547. If they were exactly .547 OD they wouldn't fit in a .547 slide tube.

Yes, maybe the TR150 inner slide was a little bigger, like 0.542 inch..? But it was definetely smaller than 0.547 inch because your largebore pressfit leadpipes didn't fit in. By the way you made me special 8H nickel leadpipe that fits my TR150 some time ago. I sent you the spec of (very) approx OD of stock TR150 pipe and you made me smaller OD version of normal largebore pipes. It fitted very well and I enjoyed the pipe.(But I sold the horn eventually.)

Yes, I remember that now. So I guess the tubes were smaller when your TR150 was made. I usually need to make leadpipes .005" smaller or more that the bore of the slide tube in order for them to fit.