This is the Maintenance Kit ONLY for the MPG401 All Metal Seal, Inverted Magnetron Pirani Gauge. Maintenace Kit Includes: seal HNV100 (9X1.6), centering ring, ignition aids. For detailed instructions on how to replace MPG400/401 maintenance kit parts, see .pdf below, pages 17 thru 23. (This pricing is for the Repair Kit Only, pumps, controllers, sensors sold separately.)