As a result of a closed tubular body shell, the electromagnetic field generated by the coil is basically no leak, so push pull it produces can be greatly improved, built-in high-precision self-lubricating bearings, to ensure no radial runout, wear resistance has also been significantly improved, so life than similar products can improve more than 30%, while the outer tube closed solenoid play a very good protection, summary, these narrow tube magnet for space, power demanding, relatively harsh environment conditions apply.