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Through hole slip rings are widely used in industry , agriculture , military, the inner hole can be from 5mm to 1000mm, and the wires can be up to 200, transfer power and different signal, including very high speed data . this model is popular to auto-wrap machine, sea /satellite antenna , crane , etc...
link:http://www.btslipring.com/through-hole-slip-ring-1
Through hole slip ring