Forget iOptron and Vixen. I ordered this...
https://on-stage.com/products/view/11140/471270
...and from a Reverb.com seller, similar to eBay, but for that musical only, for US$21.57, shipped.
We'll see how that flies.
Here are a couple of reviews I found online, at least one pertaining to that astronomical instead...
"
I really had no need for the 11 lb Celestron weight and some one told me about these. They fit right on the weight bar and you do not have to remove the safety knob at the bottom to install and remove them. With the 3 lb and the 6 lb, I have all the weight I need right now, Plus they are smaller around, so you can move them all the way to the top and not worry about hitting anything on the mount. The lock knobs have a soft plastic or rubber tip, so it will not mark up the bar." - Michael
I assume that they have an "AVX", at least.
Then there was this one...
"
Perfect size and weight for the Impact boom stands. No more hassles no matter how big the reflector used." - mediclimber
That had me confused, at first. All of that has to do with lighting. Of course, the rest of you probably knew that already.