Smallest reloading die nuts, for progressive presses where dies are close together.

What is the smallest available nut that fits onto a standard 7/8" 14 thread as is used on most reloading dies?
I've got lots of different "nuts", round, hex, large, small....    and it's difficult to tighten or loosen them.
My reloading press is an RCBS Pro2000. 

Any advice on the smallest ones commercially available - and where to buy them?

Good question, I've recently found that on my XL650 toolheads, when using Lee Dies, they are not long enough to fit even Dillon narrow/thin nuts on top. Another thread suggested putting the nuts on the exposed thread underneath, but then I discover that they can interfere with the press frame and compromise toolhead position.

I've just received an RCBS die with their round, knurled, "nut" with the setscrew - maybe those are favourite?

I expect that others, with much more experience than me, will chime in on this one.

The Dillon 1" is.probably the smallest nut.
. They have a special.wrench for them

There are long, custom wrenches that look like deep sockets which preclude having to get down near the nut with any sort of tool.  I don't recall who makes them. A quick search and you'll get sorted out.

I do install locking nuts underneath of the toolheads on XL650s. Very often I install nuts on both ends of toolhead, especially on sizing/depriming stations, in order to avoid dies going lose. Lee aluminum nuts with O-ring go away as soon as I remove dies from packaging. I don't like Dillon's as well, - thread on them is partial, so dies get lose easily. I replace nuts with my own. No you cannot buy them, - too expensive to make them on CNC. However search eBay for Panel or Jam Nut - There is a company in IN that makes them, and it is better quality then Dillon.
AP

The smallest is the Dillon at approx 1 inch across the flats.  They aren’t the strongest but they work.  Best way to get at them is with a thinned deep socket.

Since your press is RCBS I would think that RCBS lock rings would be ideal. Those are 1-3/16 across the flats.

I use the Dillon nuts on my RL550 but the wrench they sent me sucks it is poorly made I am looking for a better 1 inch wrench, it is to soft and the opening on mine veries 1.010 to 1.040
sloppy and un even!

Uniquetek has a boxed end wrench made for the 1"

I'm pretty sure I already have their wrench - but I never got around to buying the nuts.