[mykeal]

I have two Walkers (2007 Uberti and 1997 ASM) and two Dragoons (1981 Uberti 2nd Model and Colt Signature 3rd Model). All 4 guns take nipples with 1/4x28 threads.

Treso makes at least three different size nipples with 1/4x28 threads: 11-50-01 (0.635" long), 11-50-11 (0.494" long) and 11-50-13 (0.538" long). The other difference between these three is the size of the wrench shoulder - the distance across the flats that the nipple wrench must fit in order to install/remove the nipples.
11-50-01: 0.215"
11-50-11: 0.175"
11-50-13: 0.215"
Finally, the diameter at the top of the nipple:
11-50-01: 0.160"
11-50-11: 0.151"
11-50-13: 0.160"

The OEM nipples in my 4 'horse pistols' are all different lengths:
Uberti Walker: 0.627"
ASM Walker: 0.640"
Uberti 2nd Dragoon: 0.610"
Colt 3rd Dragoon: 0.633"

The distance across the wrench flats:
Uberti Walker: 0.176"
ASM Walker: 0.182"
Uberti 2nd Dragoon: 0.174"
Colt 3rd Dragoon: 0.176"

All the above suggests to me that the correct Treso part number for the large frame Colt replica revolvers is 11-50-01; the 11-50-11 and 11-50-13 are both too short. However, the 11-50-01 and the 11-50-13 won't fit the Walker nipple wrench; both are too wide and the -01 is too long. I guess I'd conclude that Thunder Ridge's catalog is incorrect, at least based on the hardware I have at present.

Now, as to cap sizes, measured several each of the following this morning; the numbers are averages, the first is the size of the opening, the second is the height:
CCI #10: 0.160", 0.160"
CCI #11: 0.166", 0.162"
Remington #10: 0.167", 0.168"
Remington #11: 0.166", 0.145"
RSW #1075: 0.165", 0.154"

That data suggests that either CCI size should fit the Walker and Dragoon OEM nipples, while both the Remingtons sizes and the RSW are too large. I said suggests, because the taper of the nipple cone and the cap matter greatly. And I can't measure that with my workbench equipment.

So, let's put some caps on some nipples:
Uberti Walker OEM: CCI #10, yes, CCI#11, no, Remington #10, yes, Remington #11, no, RSW #1075, no (no means too loose).
ASM Walker OEM: CCI #10, no, CCI #11, no, Remington #10, no, Remington #11, no, RSW #1075, no (all were too loose, would have to be pinched to fit).
Uberti 2nd Dragoon OEM: CCI #10, yes, CCI #11, no, Remington #10, no, Remington #11, no, RSW #1075, no (no means too loose).
Colt 3rd Dragoon OEM: CCI #10, no (too tight), CCI #11, yes, Remington #10, no (too tight), Remington #11, yes, RSW #1075 no (too tight).
Treso 11-50-01: CCI #10, yes, CCI #11, no, Remington #10, no (almost, just a little loose), Remington #11, no, RSW #1075, no (almost, just a little loose).
Treso 11-50-11: CCI #10, no (too tight), CCI #11 no (almost, just a little loose), Remington #10, no (almost, just a little loose), Remington #11, no (almost, just a little loose), RSW #1075 yes.
Treso 11-50-13: CCI #10, no (too tight), CCI #11, yes, Remington #10, yes, Remington #11, yes, RSW #1075, no (too tight).

What does all this mean? I have too much time on my hands. Actually, it doesn't mean a great deal. Nipples and caps seem to vary considerably, so you really just have to try them out and see what they do. I don't think there is a simple answer for any given gun design, as the nipples they use one year may come from a different supplier another year. And as for nipples themselves, there just is no spec except for thread size. Notice that the suppliers do not specify the length, shape of the cone (including the opening at the top), distance across the flats or even recommended cap size, all of which matter. Finally, as for the caps, I can't discern any commonality with respect to designated size between manufacturers, so specifying a given cap size essentially means nothing without also specifying the manufacturer; a #10 from CCI is not a #10 from Remington, and who knows where RSW falls in.

Have a nice day.