Plow blades come on two different styles.
Chute blade: Chute blades have a hollow tube or "chute" on the back of the blade. The cable or conduit being installed runs down this chute and out the back of the blade, placing it at a specified depth. Plow machines using chute blades typically have a reel carrier attachment that carries the product to be installed while the machine is plowing.
Pull blade: Pull blades have a bell or "bullet" on the bottom of the blade that displaces the soil and creates a hole for the installed product to pass through. Unlike chute blades, this blade style pulls the product through the ground, much like directional drilling. This blade style is typically used in large diameter installations than chute blades.