Hollow impeders are available in both through flow & return flow configurations, and in many combinations of inside & outside diameters. These impeders are used for I.D. flash control with hydraulic or mechanically actuated heads, where integral mandrel impeders are generally unsuitable. Other applications include internal painting & coating of welded tube, in-line bright annealing & special instrumentation tubing where wiring or optical fibre is laid inside the tube during production. We recommend against using a larger impeder I.D. than necessary, since this reduces the amount of ferrite in the impeder & may lower efficiency. It also increases the cost.