Vacuum switch - 1/8" NPT threaded (same as most pressure switches) - for use on spa heaters installed into the suction side of a pump, which ordinarily prevents the operation of a pressure switch (fitted to most modern spa heaters). Perfect when retrofitting a new system to replace some Paramount In-Line Spa Heaters and Splash Pool Accessories heaters which are often found in the suction plumbing Single Pole, Double Throw - Normally Open and Normally closed contacts. 25A, 250v