I’m making a project which involves a rod which can slide freely in and out of a tube. However, on the edge of the tube, I’d like a device that can grasp onto or brake the rod and stop it from moving. The device would be controlled by an Arduino which is communicating with a PC. The device would only have to be able to prod downwards and hold and thereafter at some point retract. If applying pressure is an issue it could otherwise be something that prods into premade crevices of some sort along the rod. I’ve attached a diagram of what I had in mind. My question is simply what kind of components I could use to make it.