approx 8oz (227g) depending on position (see below)
The Plamp II will hold 12” reflectors and diffusers in any position with confidence.
20” reflectors, generally held in most positions and not fully cantilevered out, can be held and positioned confidently with a single Plamp II.
20” Diffusers can be cantilevered above your subject using one Plamp, however it is pushing the limits of the Plamp’s holding capacity.
It might take some experimentation to find a position that will hold.
For diffusers larger than 20” in diameter, two Plamps are pretty much required to hold it steady.