A jig for selecting a valve part number or a joint part number representing respective selected conditions required for selecting a valve or a joint comprising: a substantially rectangular base plate defining an inner space, and several sliding gauges laterally arranged in the inner space to slide in a longitudinal direction of the base plate, each of the sliding gauges comprising a condition description area including several conditions thereon from which the selected condition is determined, and a symbol description area including several symbols thereon, both the conditions and the symbols arranged in the sliding direction, several condition selecting windows laterally arranged, each of the condition selecting window being configured to expose one of the selected conditions, several symbol selecting windows laterally arranged, each of the symbol selecting window being configured to expose one of the selected symbols.