The legendary PD-55. For nearly 40 years, the PD-55 and its predecessor – the PD-50 have been the productivity leaders in post driving. At just 54 pounds and with a 3-1/2in. piston, the brutally tough PD-55 is capable of handling your toughest applications quickly and efficiently. The PD-55 is ideally suited for driving t-posts, ground rods, tent stakes, grape stakes, delineator posts, form pins and fence posts up to 3-5/8in..