Touchscreens today represent the most versatile solution for configuring user interfaces. A toll for this versatility is the intangibility of the displayed virtual controls. The addition of haptic feedback can improve their manipulation by reinforcing or even substituting visual information. While haptic rendering of virtual buttons is advancing, tangible knobs seem yet to come, possibly due to the inherent difficulty to conceptualize rotation as an interaction primitive in absence of a physical control. To address this issue, we propose a hybrid solution consisting in an endless knob with programmable resistance to rotation. Compared to existing related devices, it minimizes costs, encumbrance and power consumption, making its installation also possible on portable equipment. After describing its design and main features, we present a test which assessed how haptic feedback rendered by the knob affects performance in a visual target-matching task: users had to select targets placed on a horizontal slider by dragging its cursor through knob rotation. Results show that haptic augmentation significantly improved target acquisition.