Lots of people use weightlifting weights to add extra mass to their mount counterbalance, but the 1" diameter holes mean they are a sloppy fit, even when sandwiched between two 'normal weights'. This creates the opportunity for them to slip, jarring the mount and possibly spoiling a sub.
Here's a solution - 3D printed bushes.The bushes fit neatly in standard weights and fit standard 18mmm or 20mm shafts and should suit most Synta (Celestron and Skywatcher) and many other mounts.
Download the STL files from the links below:
And here are some custom sizes that have been requested - not that all adaptors are sized to be free on the shafts rather than tight fits.