These precision tungsten filaments for Topcon(R)/ISI(R) and ETEC(R) SEM's are made to meet or exceed original manufacturer's specifications. It is especially difficult to find the ETEC filaments due to the precision required to manufacture them. These filaments are brand new -- not rebuilt -- so there is no need to send in your old ceramic bases. In addition, the stability exceeds most rebuilt products and the price is comparable. They are packaged in boxes of 10 filaments. These filaments are virtually always in stock, ready to ship -- even the ETEC models!