A new series of magnetic clutches and couplings from Sterling Instrument feature no friction or wearing parts, uses no electricity and no magnetic particles to leak. These units, identified as the S90MCC-MTL Series, are stock in seven different bore sizes: 0.250", 0.375", 0.500", 0.625", 0.750", 0.875" and 1.000". Unit length range from 1.65" to 3.11". Their torque range is fron 0.06 lbs-in. to up to 25 lb.-in. Weight ranges from 0.73 lbs to 8.95 lbs.

Other features include repeatable torque control, easy adjustment and application, continuous slip, zero stick slip and smoothness without friction. 

http://www.sdp-si.com/estore/CoverPg/Clutches.htm

Applications include material handling for conveyor belts, film transport, capping of syringes or bottles, shrink wrapping, constant wire tension coil winding, film tensioning and toruqe limiting.