Single-acting Hollow Plunger Cylinders  Hollow Plunger Cylinders  Hollow plunger design allows for both pull and push forces  Singer-acting,Website:http://www.dudemachinery.com, spring return  Nickel-plated, floating centre tube on models over 20 ton  increases product life.  Baked enamel finish for increased corrosion resistance  Collar threads for easy fixture  RCH-120 has 1/4" NPT oil port and includes AR-630 coupler  RCH-121 and RCH-1211 have FZ-1630 coupler and AR-630  quick coupler, other models have CR-400 coupler.