bob540, I did not seek a specialty audio product, just as I did not seek a high end rack for my gear. I have made choices where to allocate the funds, and I prefer to allocate them in the actual power and audio chain. Note, however, that I am doing digital source only, and would likely have a different perspective if I did analogue.
I say this to give you some perspective on my advice. I use rubber hockey pucks under speakers occasionally for the same reason; cheap, effective, and allows quick changes which I do continuously. Were the speakers anchored to one spot always, I would probably use spikes. But, it's not practical for moving about.
I would look for spikes used for large furniture, such as big cabinets. Maybe check with a furniture store, or an office store. It's pretty easy to get larger, black ones with wider/double wheels. Mine have the twin wheels per caster with a gap between (like dual wheels on a pickup truck), and they are more than 1" wide so as to roll on the carpet easier. I think I got the casters I put on the Vapor Audio Joule White speakers at Home Depot. Tried to get better quality ones among the selections. They came with longer threaded posts than I was searching for; no problem, I added washers to close the gap, and frankly, the speakers are better sounding with the extra inch or so of elevation as it lifted the soundstage very nicely.
For the large, 175 pound amps I put on modified furniture dollies, they had solid hard rubber casters built in perhaps close to 1" thick. I can push the amps around pretty easily, even though the flooring is thick pad with thick berber carpeting. So, 60 pounds should be quite easy with wide casters, no issues. Except, watch out if the speakers are taller and thinner! You don't want them tipping when moving. Sitting still, no problem, but have a good handle on them while moving, because if they are narrow, they will tilt most likely as you move them on carpeting!
Take a spike along, and match up the thread. Take your pick on size of caster, and how long the threaded post to insert. There are only so many sizes of posts with specific wheels, so you have to be somewhat flexible. It's not hard.