So you want to work on your forearms and grip? The SideWinder Pro XTREME can help. It measures only 2 inches in diameter but provides you with thick grip training without a weight plate. The device has roller bearings that can support 2000 pounds. You can control the resistance by turning the built-in calibrated tension gauge.
To get started, just wind the handles and twist them with one or both hands. You get to use clockwise and counterclockwise motions to build strength in your body. Sets you back under $150.