Have some Onstage CW-3 counterweights. Approximately 3lb (~1.3kg) each.
Adjustable screw with nylon tip. Will fit shafts from 14mm to 22mm. Worked perfectly on my Celestron AVX shaft.
Handy when you need to add on a tiny bit of extra weight. Not needed any more as I finally had to bite the bullet and add a second full sized counterweight.
Got them from Amazon here:
https://www.amazon.com.au/On-Stage-C.../dp/B0010HHAXC
$15 each