A replacement BCD dump valve knob. Some of these are very difficult to grasp when wearing gloves and, if black, difficult to spot. Based on the ScubaPro original shown in the photos.

Slightly positively buoyant in the supplied profile but the infill can be increased if you want to make less buoyant.

Works well in PLA but if you want a more rugged version then you can easily print in materials such as TPU.

The hole for the cord is just under 1.75mm but can be drilled out if that's too tight. Only suitable for dump pulls that end in a knot which you've obviously got to be able to untie to remove original.