The PTO assembly begins with this type of yoke. It is connected to the tractor and then used to attach the driveline. There are two main types of tractor yokes. The first type is a spring-lok, which uses a spring-loaded collar to attach and release the yoke and the second type is a quick disconnect, which uses a push-pin mechanism for connectivity.
The tractor yoke can also be designated as 6-spline, 20-spline or 21-spline representing how it matches to the connection on the tractor.