The NTE6407 thru NTE6412 are bilateral trigger DIACs offering a range of voltage characteristics from 28V to 63V. These devices are triggered from a blocking–to–conduction state for either polarity of applied voltage whenever the amplitude of applied voltage exceeds the breakover voltage rating of the DIAC.
 
Full spec sheet:
https://www.nteinc.com/specs/6400to6499/pdf/nte6407.pdf