The CV402 is a protective spark gap. The commercial Type designation appears on the base as GXA80.
The KB/QG identifies this valve as being made to specification K1001 or K1006, the B denotes qualification by a UK authority and the QG identifies the maker as English Electric Valve Co., location unknown.
The construction has two metal discs carrying the gap points and a surrounding ceramic tube.
Indistinct stamps on the base.
The wide glass tube envelope is 30 mm in diameter and, excluding the IO base pins, is 62 mm tall.