Shaft Couplers
Shaft couplers simply connect two shafts together. The primary purpose to transfer torque from one shaft to another, and whilst doing so it can correct for misalignment between the shafts and account for shock loads by flexing or slipping. To do so, many shaft couplers have a spring like component in the middle, allowing it to bend and stretch to conform to the shaft placement. Most also attach to the shafts with either a set screw or a clamp. You can find them at https://www.mcmaster.com/shaft-couplings, and more details at https://www.thomasnet.com/articles/hardware/coupling-types/.