Have a look at the clamps and fitting used to attach dial indicators to the stem of a magnetic base. They are around 7/16" diameter not 1/2" but they perform a similar function of adjustment.

Alternatively if there is a place near you that supplies wheelchairs you may find they have clamps and fittings for attaching small switches to wheelchairs so people can activate them with their head.

Another alternative could be the clamps and fitting used to build equipment setups in chemistry laboratories.