The following chart gives you the industry standard for PTO driveline horepower ratings.  Please keep in mind these are rated horsepower at the PTO, not engine horsepower.  Many times the difference between engine horsepower and PTO horsepower can vary as much as 10%.  These values give the maximum recommended horsepower that can be transferred through the drivelive from the tractor to the implement.

Series Rating @ 540rpm Rating @ 1000rpm
1 16 24
2 21 32
3 30 47
4 35 54
5 47 72
6 62 98
7 74 114
8 91 145
9 141 225
 

If you are not sure how how far you can safely extend a driveline, the following chart give the recommended maximum extension available on each series of shaft with a minimum collapsed lenth listed.  In most cases, it is recommended that the driveline does not extend 1/2 of its’ collapsed length.  This means the driveline tubes should should overlap at least 1/2 for safe operation at all speeds.

 

Minimum Collapsed Length (L)

  28″ 31″ 35″ 39″ 43″ 47″ 51″ 55″ 59″
Series

Maximum Extended Length (L)

1 35″ 41″ 47″ 53″ 59″ 64″ 71″ 77″ 83″
2 35″ 41″ 47″ 53″ 59″ 64″ 71″ 77″ 83″
3 35″ 41″ 47″ 53″ 59″ 64″ 71″ 77″ 83″
4 35″ 41″ 47″ 53″ 59″ 64″ 71″ 77″ 83″
5 34″ 40″ 46″ 52″ 58″ 63″ 70″ 76″ 82″
6 34″ 40″ 46″ 52″ 58″ 63″ 70″ 76″ 82″
7 34″ 40″ 46″ 52″ 58″ 63″ 70″ 76″ 82″
8 34″ 40″ 46″ 52″ 58″ 63″ 70″ 76″ 82″
9 33″ 39″ 45″ 51″ 57″ 62″ 69″ 75″ 81″
 
All length measurements are U-joint to U-joint, with the PTO shaft completely collapsed/closed.
 
Overrunning Clutch, Also known as the freewheel mechanisms, this type of clutch disengage the driveshaft from the driven shaft, when the driven shaft rotates faster than the driveshaft. An example of such a situation can be when a cyclist stops peddling and cruises. However, in case of automobiles going down the hill, you cannot take your feet off the gas pedal, as there is no free wheel system. If you do so, the whole engine system can be damaged.
 
Disc Clutch or  Safety Clutch Also known as the torque limiter, this device allows a rotating shaft to “slip” or disengage when higher than normal resistance is encountered on a machine. An example of a safety clutch is the one mounted on the driving shaft of a large rotary cutter . If a stone or something else is encountered by the grass mower, it stops immediately and does not hamper the blades.