[Adjustable Resistance]The resistance strength of this power twister can be adjusted by rotating the knob,the range is:22-440lbs,2-20 levels. [Hydraulic Pressure Protection]Research shows it is very dangerous to use spring power twister,because its springback is violent,easy to hurt you; the spring in the middle easily pinch youself; the spring is prone to break after prolonged use. Please throw away those spring power twister,try our hydraulic power twister which is and more becasue of the patented hydraulic adjustment system principle. There is no danger of the spring breaking,'t rebound and hurt yourself! [Totally-enclosed Hydraulic Cylinder]Unlike other spring based exercisers,our power twister adopts totally-enclosed hydraulic cylinder which offers you stable resistance strength, not weaken over time! movements,and what's more,you can fully open your arm even you reduce the resistance! [Double Carbon Steel]Our hydraulic arm exerciser is made of high-density double carbon steel,engineering plastics and hydraulic cylinder,which passed 100000 endurance tests,'t easily be deformed and broken! Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.